Insomnia...

What means this heaviness that hangs upon me?
This lethargy that creeps through all my senses?
Nature, oppress'd and harrass'd out with care,
Sinks down to rest.
- Joseph Addison, Cato (act V, sc. 1)

What probing deep
Has ever solved the mystery of sleep?
- Thomas Bailey Aldrich, Human Ignorance

But I, in the chilling twilight stand and wait
At the portcullis, at thy castle gate,
Longing to see the charmed door of dreams
Turn on its noiseless hinges, delicate sleep!
- Thomas Bailey Aldrich, Invocation to Sleep

He sleeps well who is not conscious that he sleeps ill.
- Francis Bacon