The underlying cause of<unk>  remains enigmatic. The leading hypotheses are some form of epileptic event, a problem with blood circulation around, to or from the brain, or some kind of migraine-like phenomenon. The differences are sufficiently meaningful that transient amnesia may be considered a heterogeneous clinical syndrome with multiple etiologies, corresponding mechanisms, and differing prognoses. Precipitating events<unk>  attacks are associated with some form of precipitating event in at least one-third of cases. The most commonly cited precipitating events include vigorous exercise (including sexual intercourse), swimming in cold water or enduring other temperature changes, and emotionally traumatic or stressful events. There are reports of<unk> -like conditions following certain medical procedures and disease states. One study reports two cases of familial incidence (in which two members of the same family experienced<unk> , out of 114 cases considered. This indicates the possibility that there could be a slight familial incidence. If the definition of a precipitating event is widened to include events days or weeks earlier, and to take in emotionally stressful burdens such as money worries, attending a funeral or exhaustion due to overwork or unusual childcare responsibilities, a large majority, over 80%, of<unk>  attacks are said to correlate with precipitating events. The role of psychological co-factors has been addressed by some research. It is the case that people in a state of<unk>  exhibit measurably elevated levels of anxiety and/or depression. Emotional instability may leave some people vulnerable to stressful triggers and thus be associated with<unk> . Individuals who have experienced<unk> , compared with similar people with TIA, are more likely to have some kind of emotional problem (such as depression or phobias) in their personal or family history or to have experienced some kind of phobic or emotionally challenging precipitating event. Vascular hypotheses Cerebral ischemia is a frequently disputed possible cause, at least for some segment of the<unk>  population, and until the 1990s it was generally thought that<unk>  was a variant of transient ischemic attack (TIA) secondary to some form of cerebrovascular disease. Those who argue against a vascular cause point to evidence that those experiencing<unk>  are no more likely than the general population to have subsequent cerebral vascular disease. In fact, "in comparison with TIA patients,<unk>  patients had a significantly lower risk of combined stroke, myocardial infarct, and death." Other vascular origins remain a possibility, however, according to research of jugular vein valve insufficiency in patients with<unk> . In these cases<unk>  has followed vigorous exertion. One current hypothesis is that<unk>  may be due to venous congestion of the brain, leading to ischemia of structures involved with memory, such as the hippocampus. It has been shown that performing a Valsalva maneuver (involving "bearing down" and increasing breath pressure against a closed glottis, which occurs frequently during exertion) may be related to retrograde flow of blood in the jugular vein, and therefore, presumably, cerebral blood circulation, in patients with<unk> . Migraine A history of migraine is a statistically significant risk factor identified in the medical literature. "When comparing<unk>  patients with normal control subjects… the only factor significantly associated with an increased risk for<unk>  was migraine." Fourteen percent of people with<unk>  had a history of migraine in one study, and approximately a third of the participants in another clinical study reported such a history. However, migraine does not appear to occur simultaneously with<unk>  nor serve as a precipitating event. Headache frequently occurs during<unk> , as does nausea, both symptoms often associated with migraine, but it appears that these do not indicate migraine in patients during a<unk>  event. The connection remains conceptual, and muddied further by a lack of consensus about the definition of migraine itself, and by the differences in age, gender, and psychological characteristics of migraine sufferers when compared to those variables in the<unk>  cohort. Epilepsy Amnesia is often a symptom in epilepsy, and for that reason people with known epilepsy are disqualified from most studies of<unk> . In a study where strict criteria were applied to<unk>  diagnosis, no epileptic features were seen in EEGs of over 100 patients with<unk> . However, despite the fact that EEG readings are usually normal during a<unk>  attack, and other usual symptoms of epilepsy are not observed with<unk> , it has been speculated that some initial epileptic attacks present as<unk> . The observation that 7% of people who experience<unk>  will develop epilepsy calls into question whether those case are, in fact,<unk>  or transient epileptic amnesia (TEA). TEA attacks tend to be short (under one hour) and tend to recur, so that a person who has experienced both repeated attacks of temporary amnesia resembling<unk>  and if those events lasted less than one hour is very likely to develop epilepsy. There is additional speculation that atypical cases of TEA in the form of nonconvulsive status epilepticus may present with duration similar to<unk> . This may constitute a distinct subgroup of<unk> . TEA, as opposed to "pure"<unk> , is also characterized by "two unusual forms of memory deficit …: (i) accelerated long-term forgetting (ALF): the excessively rapid loss of newly acquired memories over a period of days or weeks and (ii) remote autobiographical memory loss: a loss of memories for salient, personally experienced events of the past few decades." Whether an amnestic event is<unk>  or TEA thus presents a diagnostic challenge, especially in light of the recently published descriptions of possible long-term cognitive deficits with (presumably correctly diagnosed)<unk> . Other putative associations There have been assertions of a possible link between<unk>  and the use of statins (a class of drug used in treating cholesterol). En bloc memory loss which is total, permanent, and irrecoverable can occur as an alcoholic "black out," usually lasting longer than an hour and up to 2–5 days. Marijuana intoxication, Halogenated hydroxyquinolines such as Clioquinol, PDE inhibitors such as sildenafil, Digitalis and scopolamine intoxication, and general anaesthesia have been reported with<unk> .
Transient global amnesia
Childhood amnesia
Excited delirium
Transient epileptic amnesia
Emergence delirium
Drug-induced amnesia
Post-traumatic amnesia
Psychogenic amnesia