The mind does not pass suddenly and at a bound from the condition of dream-fancy to that of waking perception.

I have already had occasion to touch on the "hypnagogic state," that condition of somnolence or "sleepiness" in which external impressions cease to act, the internal attention is relaxed, and the weird imagery of sleep begins to unfold itself.

And just as there is this anticipation of dream-hallucination in the presomnial condition, so there is the survival of it in the postsomnial condition.

As I have observed, dreams sometimes leave behind them, for an appreciable interval after waking, a vivid after-impression, and in some cases even the semblance of a sense-perception.
If one reflects how many ghosts and other miraculous apparitions are seen at night, and when the mind is in a more or less somnolent condition, the idea is forcibly suggested that a good proportion of these visions are the _debris_ of dreams.

In some cases, indeed, as that of Spinoza, already referred to, the hallucination (in Spinoza's case that of "a scurvy black Brazilian") is recognized by the subject himself as a dream-image.[101] I am indebted to Mr.W.H.Pollock for a fact which curiously illustrates the position here adopted.