Full Idea
Since when we sleep the senses are closed, mind is separated from its surroundings and loses the power of memory. When we wake the mind re-contacts the world, and regains the power of reason.
Gist of Idea
When we sleep, reason closes down as the senses do
Source
report of Heraclitus (fragments/reports [c.500 BCE], A16) by Sextus Empiricus - Against the Professors (six books) 7.130
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.44