Physiologically, sleep paralysis is closely related to REM atonia, the paralysis that occurs as a natural part of REM (rapid eye movement) sleep. Sleep paralysis occurs either when falling asleep, or when awakening. When it occurs upon falling asleep, the person remains aware while the body shuts down for REM sleep, and it is called hypnagogic or predormital sleep paralysis. When it occurs upon awakening, the person becomes aware before the REM cycle is complete, and it is called hypnopompic or postdormital.[5] The paralysis can last from several seconds to several minutes, with some rare cases being hours, "by which the individual may experience panic symptoms"[6] (described below). As the correlation with REM sleep suggests, the paralysis is not entirely complete; use of EOG traces shows that eye movement is still possible during such episodes.[7] When there is an absence of narcolepsy, sleep paralysis is referred to as isolated sleep paralysis (ISP).[8] In addition, the paralysis may be accompanied by terrifying hallucinations (hypnopompic or hypnagogic) and an acute sense of danger.[9] Sleep paralysis is particularly frightening to the individual because of the vividness of such hallucinations.[8] The hallucinatory element to sleep paralysis makes it even more likely that someone will interpret the experience as a dream, since completely fanciful or dream-like objects may appear in the room alongside one's normal vision. Some scientists have proposed this condition as an explanation for alien abductions and ghostly encounters.[10] A study by Susan Blackmore and Marcus Cox (the Blackmore-Cox study) of the University of the West of England supports the suggestion that reports of alien abductions are related to sleep paralysis rather than to temporal lobe lability.[11] Some authors have warned of the possible misconnection between child sexual abuse (CSA) and hypnagogic/pompic phenomena and have noted that some clients after having described such an event to a fortune teller or psychic that the psychic may have suggested CSA.[12][13]