Nearly half of people with dysthymia have a symptom that also occurs in major depression, shortened REM latency — that is, they start rapid eye movement (vivid dreaming) sleep unusually early in the night.
from the February 2005 issue of the Harvard Mental Health Letter
When I read this, I laughed as I said to myself ‘Not me! I don’t go to sleep early enough for this!’. Then I laughed some more because only I would tell myself a joke that bad.