John Dryden - Dreams

Dreams are but interludes which Fancy makes;
When monarch Reason sleeps, this mimic wakes:
Compounds a medley of disjointed things,
A mob of cobblers, and a court of kings:
Light fumes are merry, grosser fumes are sad;
Both are the reasonable soul run mad;
And many monstrous forms in sleep we see,
That neither were, nor are, nor e'er can be.
Sometimes forgotten things long cast behind
Rush forward in the brain, and come to mind.
The nurse's legends are for truths received,
And the man dreams but what the boy believed.
Sometimes we but rehearse a former play,
The night restores our actions done by day;
As hounds in sleep will open for their prey.
In short, the farce of dreams is of a piece,
Chimeras all; and more absurd, or less.

John Dryden

http://www.poemhunter.com/poem/dreams-460/