Henry Fuseli Sleep paralysis, or more properly, sleep paralysis with hypnagogic and hypnopompic hallucinations have been singled out as a particularly likely source of beliefs concerning not only alien abductions, but all manner of beliefs in alternative realities and otherworldly creatures. This may last a few seconds or several moments, occasionally longer. An intense sense of dread and terror is very common. The presence is likely to be vaguely felt or sensed just out of sight but thought to be watching or monitoring, often with intense interest, sometimes standing by, or sitting on, the bed. On some occasions the presence may attack, strangling and exerting crushing pressure on the chest.
People frequently try, unsuccessfully, to cry out.
After seconds or minutes one feels suddenly released from the paralysis, but may be left with a lingering anxiety. Extreme effort to move may even produce phantom movements in which there is proprioceptive feedback of movement that conflicts with visual disconfirmation of any movement of the limb. People may also report severe pain in the limbs when trying to move them. For a summarry of SP Characteristics see Table 1 . Our research has led us to conclude that hallucination is probably not too strong a term for the experiences associated with sleep paralysis.