Our circadian rhythms—that is, our biological clocks—cause our body temperature to drop very slightly right when we go to bed, which makes us sleepy and helps us doze off. It gets lower and lower as we continue to sleep, until about two hours before we wake up, when it rises again. Keeping your room cool (not cold) supports that internal thermostat. Try to avoid extremes on either end, as both super hot and frigid temps can disrupt beauty rest.

MORE: Sleep Well In Sweltering Summer Heat