In "The Ominous Numinous Sensed Presence and ‘Other’ Hallucinations," (Journal of Consciousness Studies, 8, No. 5–7, 2001), author J. Allan Cheyne describes how "Virtually everyone has had, at some time, the experience of feeling that he or she was not alone, despite otherwise confident knowledge that there really was no other person nearby. This feeling may range from a vague almost embarrassingly unwarranted suspicion to a feeling of absolute certainty."

Just when you think we're about to enter a land or spirits – good or evil – he abruptly shifts gears and describes a scientific reason for these experiences:

"In recent work quantitative analyses have provided evidence that the sensed presence is a common concomitant of sleep paralysis that is particularly associated with visual, auditory and tactile hallucinations, as well as intense fear (Cheyne, Rueffer and Newby-Clark 1999). Sleep paralysis itself is a conscious state of involuntary immobility occurring prior to falling asleep or immediately upon wakening. An episode may last from a few seconds to several minutes. Although individuals in this state are unable to make gross bodily movements, they are able to open their eyes and to perceive and subsequently report on external events (Hishikawa, 1976; Hishikawa and Shimizu, 1995). Recent surveys suggest that approximately 30% of young adults report some experience of sleep paralysis (Cheyne, Newby-Clark and Rueffer, 1999; Fukuda et al., 1998; Spanos et al., 1995). Out of combinations of particular sensory experiences grow elaborate and complex scenarios that have been identified as experiential sources of accounts of incubus attacks, daemonic possession, old hag attacks and, more recently, alien abductions (Baker, 1990; 1992; Cheyne, Rueffer and Newby-Clark, 1999; Firestone, 1985; Hufford, 1982; Ness, 1978; Spanos et al., 1993). These experiences are typically quite frightening and are the original referents for the term ‘nightmare’ (Liddon, 1967; Hufford, 1982).

"Sleep paralysis experiences are referred to as hypnagogic (sleep-onset) or hypnopompic (sleep-offset) hallucinations. The term hallucination is appropriate because the experiences occur while one is awake and aware of the immediate surroundings.

"These hallucinations are also, however, a form of dreaming inasmuch as they are associated with sleep-onset REM states (Hishikawa and Shimizu, 1995). Sleep paralysis hallucinations are, in effect, the superpositioning of dream imagery and affect on waking consciousness. Indeed, the various experiential features of these hallucinations are readily mapped onto known neurophysiology of REM (Cheyne, Rueffer and Newby-Clark, 1999). Of particular relevance to the present argument are recent neuroimaging studies of REM-related activation of subcortical and cortical limbic centres including the extended amygdala, nucleus basalis of Meynert in the substantia innominata, and anterior cingulate cortex (see Hobson et al., 1998 for a review of this work). As Hobson et al. note, these studies reveal ‘an unexpectedly prominent role of the limbic system in the selection and elaboration of dream plots’ (ibid., p. R1).

"The sensed presence during sleep paralysis is often experienced as ominous or threatening. This is quite consistent with the involvement of the limbic structures associated with REM. Whalen (1998) suggests that there is a ‘vigilance system’ associated with the extended amygdala and related structures such as the nucleus basalis of Meynert. The vigilance system is normally activated by an initial detection of possible danger. The vigilance system initiates procedures that monitor the environment for further cues to corroborate or disconfirm the existence of an emergency. In a similar vein, but with specific reference to consciousness, Ellis (1999) speaks of these processes as motivated interpretive activities and further notes that sensory processing remains unconscious until affective midbrain and cortical structures such as the anterior cingulate highlight particular features of the sensorium. The specific nature of those features is specified by biases, or perhaps more accurately, interests induced by the vigilance system. Evolution has selected certain environmental features as cues that warn us of things in the immediate environment that constitute a potential threat to the organism. These cues are, individually, inherently ambiguous in the absence of further corroborating evidence. Indeed, Whalen suggests that the function of the vigilance system is the disambiguation of prior warning cues. The immediate task under such conditions is to ‘flesh-out’ what is merely implied by biologically prepared cues. The resultant state of vigilance entails lowered and biased sensory thresholds for further threat cues and may set the stage for false alarms. These temporary biases are adaptive because the initial cues for danger change the a priori probabilities of immediate danger (LeDoux, 1994; 1996). The chain of events (threat cue — ambiguity — search — disambiguation) is normally accomplished quite rapidly.

"That is, environmental cues ordinarily quickly corroborate or disconfirm the existence of threat.

"Cheyne, Rueffer and Newby-Clark (1999) argue that feelings of presence such as emerge during sleep paralysis arise from the same limbic neurophysiology underlying threat detection. I suggest further that the sensed presence represents the experiential component of the resulting ambiguity. During sleep paralysis endogenous REM-based activation of the vigilance system produces, in the absence of external threat, an irresolvable ambiguity. This radical ambiguity is experienced as a protracted threatening, though insubstantial, sense of presence. The sensed presence, on this view, constitutes a liminal feeling on the edge of what Damasio (1999) has called core consciousness. It is important to note that, although external cues are absent, there is a concurrent quasi-random endogenous activation of affective, sensory and motor areas. These normally constitute the source of REM dream-imagery (Hobson and McCarley, 1977). During sleep-onset REM, the sensed presence may serve to bind and shape concurrent visual and auditory hallucinations according to the adaptive biases of the vigilance system. James (1958) explicitly treated feelings of a presence as ‘imperfectly developed’ hallucinations (p. 62). I argue further that the sensed presence may be viewed not only as the most elementary form of hallucination but also as a neuropsychological context that motivates, initiates and shapes more elaborate hallucinoid experiences. On this view, the affective qualities of the sensed presence are critical in determining the nature of the associated hallucinations."

That's a lot to digest and even after reading it several times the scientific jargon perplexes me. I think the bottom line is that there is a valid biological reason for that "sensed presence," at least according to Cheyne and others. And here I thought my experiences were powered by some other worldly entity, something into which a guy with my active imagination could sink his teeth! But wait, Cheyne continues:

"A critical claim of the argument of this paper is that the inherent ambiguity of the threat detection mechanism is, under the conditions just described, experienced as at least one aspect of what has been referred to as the numinous (Otto, 1923). Otto coined the term ‘numinous’ (numen praesens) to designate the ineffable sense of a sacred or daemonic presence. It is, for Otto, critical to a full understanding of the nature of the ‘Holy’. Although there are clearly positive beatific aspects to the numinous, Otto frequently stresses the ‘awfulness’ and the ‘dreadful’ aspects of the numinous experience. These aspects are captured in the term ‘mysterium tremendum’, the mystery before which we shudder and tremble. Otto speaks of the mysterium tremendum as ‘overpowering’, ‘dreadful’, ‘grisly’ and ‘horrible’. Otto took ‘daemonic dread’ to be that ‘religious moment which would appear to have been in every case the first to be aroused in the human mind’ (Otto, 1923, p. 132). Moreover, the experience of the numinous is one of ‘terror fraught with an inward shuddering such as not even the most menacing and overpowering created thing can instill’ (ibid., p.14). As may be inferred from the preceding quotation Otto clearly regarded such experiences as genuinely transcendent and supernatural. The present argument, however, is that the ineffable experience of the numinous may be given a straightforward naturalistic interpretation, one that provides an evolutionary basis for at least the more terrifying and daemonic aspects of religious experience. Otto, of course, would not have been satisfied to see his argument reduced to a naturalistic one. The sensed presence is, on the view offered here, the numinous in its purest form. Moreover, the subsequent hallucinations arising from the quasi-random REM-related imagery provide, at best, only a partial and incoherent resolution of the ambiguity and hence retain some of the numinous qualities of the sensed presence throughout the episode."

The second time

On the morning or February 26, 2009, I saw my wife, Lisa, off to work at 6:12 am and then quickly climbed back into bed for another hour of sleep. Since I had already gotten about seven hours of sleep during the night, I really wasn't all that tired, so I lay there, trying to fall back to sleep.

At some point I must have fallen asleep because I began dreaming of being alone in my basement, where I spotted an ice cube on top of a shelve or book case. The instant I saw the ice cube, I knew I was not alone in the house, since someone would have had to place the cube there, and recently, since it was just beginning to melt.

At the exact instant I had that thought, I felt this incredibly odd sensation, as if a force of some kind was rapidly spreading through my body, beginning at the base of my skull and traveling down by spine, ending up in my testicles (of all places!). At that point it felt like someone was giving them a good squeeze, but it didn't feel painful, just a very odd sensation of a "force" or energy surging through me. This feeling didn't frighten me, nor did seeing that ice cube and knowing I was not alone give me the willies. It was just a feeling of having someone or something work its way on (or through?) me, as if to indicate I'm not alone and it's okay. Whoever or whatever is behind this appears benevolent and perhaps is trying to send me a message.

This is the second time something like this has happened. The previous year, again, during the hour after Lisa left for work, I was in bed, lying on my stomach and had this feeling of a force (or two strong hands) pushing me down into the bed. I could swear someone was bending over me, pushing me deep into the mattress. Interestingly, I didn't wake up to see what it was. Whatever it was, I wasn't frightened by it, yet I know if I was lying in bed, reading a book and a stranger were to suddenly walk into my bedroom I'd be scared to death.

Am I being contacted by someone or something? Very strange indeed, but bring it on! It's fascinating!