Utter darkness at 5pm might fan a night owl's flame, but for some 10% to 20% of Americans, autumn's lessening light can trigger a bad case of SAD, or seasonal affective disorder. The "winter blues," caused by leftover mammalian genes that want you to hibernate, can be treated with light therapy, reports USA Today.
"It's analogous to a permanent kind of jet lag," says one scientist. SAD is more common in northern states (no shock to New Englanders), and can be quite serious—severe sufferers can become suicidal. Doctors and scientists are exploring the use of several treatments, including antidepressants and hormone therapy. "Be preventative," says one psychiatrist. "See a doctor."