On the flip side of a failure to sleep is an equally insidious sign you're not doing so hot in the mental health department: You could sleep all day and still never feel like a well-rested human being. About 15 percent of people with depression sleep too much, which can be detrimental to keeping a healthy schedule [source: Ratini]. People who sleep for longer had a higher mortality risk, as well [source: National Sleep Foundation].
Certainly, fatigue is well-recognized as a symptom of depression, and it can persist even after the depression is successfully treated [sources: Targum, Fava]. But weirdly, total sleep deprivation for one night (or missing an entire day of sleep that isn't made up) relieved depressive symptoms in 40-60 percent of treatments [sources: Giedke, Schwarzler].
Of course, this isn't to say that the cure-all for feeling blue is watching the all-night marathon of the reality show about polygamous families. Because that can really depress a person.