Sixty-one papers involving over 1,700 subjects have documented that over
half of depressed patients experience an antidepressant response to sleep
deprivation. Eighty-three percent of unmedicated depressed patients who had
an antidepressant response to sleep deprivation relapsed after one night of
sleep. Short naps can also activate severe relapses. The authors suggest
that these phenomenological observations concerning relapse with a night of
sleep or with naps after successful sleep deprivation would be compatible
with the existence of a sleep- associated depressogenic process.