A few relevant passages on dreams;
Lucretius
Book 3, 111-116
Munro Translation;
QuoteMoreover when the limbs are consigned to soft sleep and the burdened body lies diffused without sense, there is yet a something else in us which during that time is moved in many ways and admits into it all the motions of joy and unreal cares of the heart.
Bailey translation;
QuoteMoreover, when the limbs are given up to soft sleep, and the heavy body lies slack and senseless, yet there is something else in us, which at that very time is stirred in many ways, and admits within itself all the motions of joy and baseless cares of heart.
There are several passages throughout Book 4 that deal with dreams and the fleeting images that are supposed to cause them. I don't know if it's worth getting into the weeds there, but in Book 4, 962-972, we are given another insight;
Munro;
QuoteAnd generally to whatever pursuit a man is closely tied down and strongly attached, on whatever subject we have previously much dwelt, the mind having been put to a more than usual strain in it, during sleep we for the most part fancy that we are engaged in the same; lawyers think they plead causes and draw up covenants of sale, generals that they fight and engage in battle, sailors that they wage and carry on war with the winds, we think we pursue our task and investigate the nature of things constantly and consign it when discovered to writings in our native tongue.
And of course the Vatican Saying on dreams, translated by Cyril Bailey;
QuoteDreams have no divine character nor any prophetic force, but they originate from the influx of images.