As the number of daylight hours decreases in late fall and winter, the pineal gland amps up its production of melatonin
, a hormone that makes us feel sleepy. The witching hour comes early and swiftly, and with it a melatonin-induced spell of drowsiness. Add to this optimal sleep conditions: Your bed is warm and cozy; the outside world is cold and crepuscular. This is it—the best time of year to get the most sleep naturally (so long as our social calendars don't keep us up).