Hypnagogic sensations are vivid dream-like experiences that occur as one is falling asleep or waking up. Accompanying sleep paralysis can cause the sensations to be more frightening. The features of these sensations generally vary by individual, but some are more common to the experience than others:
Most common:
Vividness
Fear
Falling sensation
Sensing a "presence" (often malevolent)
Pressure/weight on body (especially the chest or back).
A sensation of not being able to breathe