This is an investigation of the psychological characteristics of males who normally obtain over nine or under six hours of sleep per 24 hours, and who function well with these unusual amounts of sleep. The study includes results from detailed sleep histories, sleep logs, psychiatric interviews, and a number of psychological tests. Short sleepers were found generally to be smooth, efficient persons with a tendency towards handling stress by keeping busy and by denial. Long sleepers were "worriers" and were chronically somewhat depressed or anxious; they scored higher than the short sleepers on most tests of pathology. This group also included some creative persons. It is suggested that the differences in sleep need may be a response to the above differences in life-style and personality and that sleep, and especially D-sleep, may have a function in restoring the brain and psyche after stress or psychic pain.
Hartmann E, Baekeland F, Zwilling GR. Psychological Differences Between Long and Short Sleepers. Arch Gen Psychiatry. 1972;26(5):463-468. doi:10.1001/archpsyc.1972.01750230073014