Dr. Harris also recommends that people who think they are excessively sleepy keep track of when the drowsiness occurs.

WSJ: Unraveling the Riddle of Too Much Sleep

The students who were excessively sleepy during the day were three times more likely to have strong depression symptoms than their well-rested peers, Dr. Siddique and his colleagues found.

CNN: Sleep deprivation linked to depression in teens

More than half of the 262 high school seniors who participated in the study were "excessively sleepy, " according to a commonly used scale that gauges how likely a person is to doze off during everyday activities such as reading, watching TV, or sitting in a traffic jam.

CNN: Sleep deprivation linked to depression in teens