A 'sensed presence' often accompanies hypnagogic and hypnopompic hallucinat
ions associated with sleep paralysis. Qualitative descriptions of the sense
d presence during sleep paralysis are consistent with the experience of a m
onitoring, stalking predator. It is argued that the sensed presence during
sleep paralysis arises because of REM-related endogenous activation of a hy
pervigilant and biased attentive state, the normal function of which is to
resolve ambiguities inherent in biologically relevant threat cues. Given th
e lack of disambiguating environmental cues, however; the feeling of presen
ce persists as a protracted experience that is both numinous and ominous. T
his experience, in turn, shapes the elaboration and integration of the conc
urrent hallucinations that often take on supernatural and daemonic qualitie
s. The sense of presence considered here is an 'other' that is radically di
fferent from, and hence more than a mere projection of the self Such a numi
nous sense of otherness may constitute a primordial core consciousness of t
he animate and sentient in the world around us.