causes of sadness

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You Dream in the Half-Light
Sleeping in dim light is a real downer, found a study at Ohio State University (on hamsters, but there's evidence that it applies to us, too). Four weeks of sleeping in a 5-lux glow—the equivalent of nightlights, streetlights, a TV or computer screen—suppressed levels of the feel-good hormone melatonin and shrank parts of the hippocampus, leading to moodiness and despondency. (Note: Depressive symptoms vanished after two weeks of pitch-dark slumber.)