An absent selfhood can be described as a sudden and complete lack of the subjective experience of one's own sense of identity. During this form of ego death, there is a profound experience of remaining fully conscious, while there is no longer an “I” experiencing one's sensory input; there is just the sensory input as it is and by itself, without a conscious agent to comment on or think about what is happening to it.
Ego death (also known as ego suppression, ego loss or ego dissolution) is the temporary experience of a partial to complete disruption of a person's sense of self, which often results in a range of profound changes to how the person perceives and interprets their otherwise usually stable sense of identity, agency, and self-hood.     
These changes can include but are not limited to any combination of the following three subcategories:
An objective selfhood can be described as the experience of the person remaining aware of the existence of oneself, while no longer perceiving themselves as integrally attached to their sense of identity. Instead of feeling that they and their sense of selfhood are a unified whole which is the subject of experience, their awareness instead feels entirely separate from it's own sense of self, as if this selfhood is now the object of experience instead of the subject.
An expanded selfhood can be described as the experience of one's sense of identity becoming constituted by a wider array of concepts than it previously did. For example, while a person may usually feel that they are exclusively their “ego” and physical body, this effect can cause their sense of identity to also include the external environment or an object they are interacting with. This results in intense and inextricable feelings of unity or interconnectedness between oneself and varying arrays of previously "external" systems. For more information on this experience, please see our comprehensive article on states of Unity and Interconnectedness
Ego death is well known for the transformative and significant impacts it can often have on a person's perception of both themselves and the world around them. These responses and alterations can occur both during the experience of ego death, but also in the hours, days, or weeks afterwards.
A few of the most common examples of this phenomenon are described and listed below:
Rejuvenation is a feeling of mild to extreme cognitive refreshment which is usually felt once the experience of ego death is over and the person has also fully recovered from the trip as a whole. The symptoms of rejuvenation often include a sustained sense of heightened mental clarity, increased emotional stability, increased calmness, mindfulness, increased motivation, personal bias suppression, increased focus, and decreased depression. At its highest level, feelings of rejuvenation can become so intense that they manifest as the profound and overwhelming sensation of being "reborn" anew. Within the context of ego death, rejuvenation often feels as if it has occurred in a manner which is akin to that of rebooting a computer.
Personal Bias Suppression
Personal bias suppression is a decrease in the personal or cultural biases, preferences, and associations a person knowingly or unknowingly filters and interprets their perception of the world through. Within the context of ego death, personal bias suppression feels as if it occurs due to some sort of baseline resetting of the contexts which the ego increasingly attributes to concepts over time. This often results in the feeling of processing concepts from a neutral perspective completely untainted by past memories, prior experiences, contexts, and biases.
Overcoming fear of death
Overcoming the fear of death is very a common conclusion and feeling that is associated with ego death, with those who have undergone ego death often reporting that they not only "experienced what it is like to die", but also became both accustomed to and substantially less afraid of the prospect. This is seemingly because the experience of letting go during ego death and willfully surrendering one's own sense of self is often likened to that of the preconceived notions that many people hold about what it is like to die.
Fear of losing control
A fear of losing control is a very common occurrence when a person that undergoes ego death is not emotionally prepared, not in an appropriate set or setting, or is simply unwilling to relinquish their sense of selfhood. During this experience, the person will often find themselves experiencing overwhelming fear and anxiety relating to the fear of losing control. This fear and anxiety is especially common in those who have not experienced ego death before.
In order to overcome this fear, it is recommended that the person does their best to stop fighting the loss of control, and simply surrender themselves to the experience of ego death. Upon successfully doing this, the person will often experience a radical and positive change in their emotional state.
Viewing the self as an illusory construct
Viewing the self as an illusory construct is commonly caused by the way in which undergoing the ego-death experience often provokes radical insight into the nature of the self. These insights may take a number of forms. For example, in the case of absent and objectified self-hood, one may conclude that the ego is not an essential component of who they are. Instead, it may come to be known as a construct of the mind, conditioned by one's history and particular circumstances.
In the case of expanded self-hood, where the experienced boundary between oneself and the external world is absent, it is common to become convinced that no such boundary ultimately exists. One may then believe that they are identical in nature to the universe as a unified whole, experiencing itself and expressing itself through a particular mind and body.
Increased openness to experience
Increased openness to experience is a change in personality that is commonly reported after the experience of ego death. This change may occur as a result of feeling less obliged to conform to a particular identity, and thus becoming more likely to engage in novel experiences.
Alternatively, those who have undergone personal bias suppression will also often find themselves more open to experiences that they may have previously disregarded due to preconceptions that were not fully grounded within reality.
Subjective differences between various substances
Within the context of psychedelic usage, ego death is most commonly triggered at heavy dosages by states of high level memory suppression which cause the person to forget who they are. At other times however it can also be triggered by or in combination with sensory overload causing the person's consciousness to be completely consumed by information and therefore incapable of maintaining a stable sense of self. Within the context of dissociative usage, however, ego death seems to be triggered at heavy dosages by increasingly intense cognitive disconnection causing a person to become entirely dissociated from cognitive functions such as the maintenance of a sense of identity.
In terms of accompanying effects, psychedelic ego death usually occurs alongside states of level 6-7 geometry and internal hallucinations of an intense and often overwhelming nature. It also often synergizes with other coinciding effects such as personal bias suppression, unity and interconnectedness, spirituality enhancement, and delusions. These accompanying effects further elevate the subjective intensity and transpersonal significance of ego death experiences.
In comparison however, dissociative ego death usually occurs alongside of high level sensory disconnection and out of body experiences, within voids or holes filled with hallucinatory structures. When compared to its dissociative equivalent, psychedelic egodeath is also typically much more likely to cause an anxious response within those who are inexperienced. This is because many people experience dissociatives as inherently calming and tranquil whereas high dosage psychedelics are quite often experienced as the opposite.
Outside of psychedelics and dissociatives, it is also possible to experience ego death under the influence of a few other classes of psychoactive compound. For example, extremely heavy dosages of deliriants such as DPH or datura can often result in ego death that is accompanied by delusions, psychosis, and external hallucinations. Along side of this, heavy dosages of salvia divinorum are extremely effective at inducing ego death that is accompanied by bizzare internal hallucinations, autonomous entity contact, and machinescapes. Although these two classes of hallucinogen function very differently on both a subjective and neuropharmacological level, both of their equivalents to ego death feel as if they stem from different forms of a break down or deterioration in the brains ability to maintain normal levels of cognitive functioning.
Throughout history there have been similar concepts that were not specifically referred to as 'ego death,' but can be seen as antecedents. These have included, but are not limited to, a wide array of similar religious and philosophical concepts such as Anatta  , Satori  , and Jhana  in Vedanta and Zen Buddhism, and Fana in Sufi Islam  .
The first literary use of the term 'ego-death' or 'ego-loss' in a context that is in line with the contemporary concept, appears to be from the book 'The Psychedelic Experience - A manual based on the tibetan book of the dead' by Timothy Leary, Ralph Metzner, & Richard Alpert  . In it, Leary describes ego-death as a product of the "complete transcendence − beyond words, beyond space−time, beyond self" experienced during the peak of the psychedelic experience. He breaks the experience up into three stages inspired by the Tibetan Buddhist bardos:
- Chikhai Bardo: ego-loss, a "complete transcendence" of the self and "game";
- Chonyid Bardo: The Period of Hallucinations;
- Sidpa Bardo: the return to routine game reality and the self.
Since the publication of this book, ego death has been defined by academics and scholars in a variety of similar ways. These definitions are listed and documented below:
- In 1964 Randolf Alnaes published "Therapeutic applications of the change in consciousness produced by psycholytica (LSD, Psilocybin, etc.) in which he defines ego death as a "Loss of ego-feeling." 
- In 1988, Stanislav Grof defined ego death as "a sense of total annihilation... This experience of "ego death" seems to entail an instant merciless destruction of all previous reference points in the life of the individual... Ego death means an irreversible end to one's philosophical identification with what Alan Watts called "skin-encapsulated ego." 
- In 2001 Carter Phipps defined ego death as "the renunciation, rejection and, ultimately, the death of the need to hold on to a separate, self-centered existence." 
- In 2007 religious studies scholar Daniel Merkur defined ego death as "an imageless experience in which there is no sense of personal identity. It is the experience that remains possible in a state of extremely deep trance when the ego-functions of reality-testing, sense-perception, memory, reason, fantasy and self-representation are repressed." 
- In 2008, Johnson, Richards & Griffiths paraphrased Leary and Grof by defining ego death as "temporarily experiencing a complete loss of subjective self-identity." 
- In 2010, the psychologist John Harrison defined ego death as a "Temporary ego death as the loss of the separate self, or, in the affirmative, a deep and profound merging with the transcendent other." 
In terms of recent scientific research, The Ego-Dissolution Inventory was developed in 2016 as a validated self-report questionnaire that allows for the measurement of ego death experiences which occur under the influence of psychedelic compounds. 
There is also an increasing amount of speculation within the psychedelic community which posits that the neurological mechanism behind ego death is tied into the way in which psychedelic substances disrupt the Default Mode Network  . This is a large scale brain network that is best known for being active when a person is not focused on the outside world and the brain is at wakeful rest, such as during daydreaming and mind-wandering.
- Lebedev, A. V., Lövdén, M., Rosenthal, G., Feilding, A., Nutt, D. J., & Carhart‐Harris, R. L. (2015). Finding the self by losing the self: Neural correlates of ego‐dissolution under psilocybin. Human brain mapping, 36(8), 3137-3153. | https://doi.org/10.1002/hbm.22833
- Nour, M. M., Evans, L., Nutt, D., & Carhart-Harris, R. L. (2016). Ego-dissolution and psychedelics: validation of the ego-dissolution inventory (EDI). Frontiers in human neuroscience, 10, 269. | https://dx.doi.org/10.3389%2Ffnhum.2016.00269
- Nour, M. M., Evans, L., Nutt, D., & Carhart-Harris, R. L. (2016). Ego-dissolution and psychedelics: validation of the ego-dissolution inventory (EDI). Frontiers in human neuroscience, 10, 269. | https://www.frontiersin.org/articles/10.3389/fnhum.2016.00269/full
- Fink, S. B. (2020). Look who's talking! Varieties of ego-dissolution without paradox. Philosophy and the Mind Sciences, 1(I), 1-36. | https://www.philosophymindscience.org/index.php/phimisci/article/view/40/1
- Milliere, R. (2017). Looking for the self: phenomenology, neurophysiology and philosophical significance of drug-induced ego dissolution. Frontiers in human neuroscience, 11, 245. | https://www.frontiersin.org/articles/10.3389/fnhum.2017.00245/full
- Britannica, T. Editors of Encyclopaedia (2007, December 5). Anatta. Encyclopedia Britannica. | https://www.britannica.com/topic/anatta
- Britannica, T. Editors of Encyclopaedia (2017, April 19). Satori. Encyclopedia Britannica. | https://www.britannica.com/topic/Satori
- Britannica, T. Editors of Encyclopaedia (2014, November 13). Dhyāna. Encyclopedia Britannica. | https://www.britannica.com/topic/dhyana
- Britannica, T. Editors of Encyclopaedia (2019, August 16). Fana. Encyclopedia Britannica. | https://www.britannica.com/topic/fana-Sufism
- What's an ego death? (Jungian psychology) - Jordan Peterson | https://www.youtube.com/watch?v=E55Z_GDVXM8
- The Psychedelic Experience: A Manual Based on the Tibetan Book of the Dead | https://books.google.com/books?id=MWkv47DIFw8C&newbks=0&hl=en&source=newbks_fb
- Alnæs, R. (1964). THERAPEUTIC APPLICATION OF THE CHANGE IN CONSCIOUSNESS PRODUCED RY PSYCHOLYTICA (LSD, PSILOCYRIN, ETC.) 1: The Psychedelic Experience in the Treatment of Neurosis. Acta Psychiatrica Scandinavica, 39(S180), 397-409. | https://doi.org/10.1111/j.1600-0447.1964.tb04952.x
- Johnson, M. W., Richards, W. A., & Griffiths, R. R. (2008). Human hallucinogen research: guidelines for safety. Journal of psychopharmacology, 22(6), 603-620. | https://doi.org/10.1177%2F0269881108093587
- Ego Death & Psychedelics By John Harrison, Psy.D. (cand) | https://maps.org/news-letters/v20n1/v20n1-40to41.pdf
- Nour, M. M., Evans, L., Nutt, D., & Carhart-Harris, R. L. (2016). Ego-dissolution and psychedelics: validation of the ego-dissolution inventory (EDI). Frontiers in human neuroscience, 10, 269. | https://doi.org/10.3389/fnhum.2016.00269
- Understanding Ego Death’s Neurobiology by Graham Reed | https://psychedelicreview.com/understanding-ego-deaths-neurobiology/