My cough is much worse at night and often prevents me from sleeping. It is not so much the daytime tiredness that I resent, but the inability to proceed uninterrupted with my dreams, to run and play with my fancies, and, at last, in the early hours of the morning, to be visited with visions like a holy madman. The dreamer is like a Delian diver, fishing for pearls from the depths of our inner sea of knowledge; and I must have solved, or rather resolved, many more problems in my sleep than in my conscious hours.

Plato: Letters to my Son