Experts usually recommend setting your bedroom thermostat between 65° and 75°F—a good guideline, but pay attention to how you actually feel under the covers. Slipping between cool sheets helps trigger a drop in your body temperature. That shift signals the body to produce melatonin, which induces sleep. That's why it's also a good idea to take a warm bath or hot shower before going to bed: Both temporarily raise your body temperature, after which it gradually lowers in the cooler air, cueing your body to feel sleepy. But for optimal rest, once you've settled in to bed, you shouldn't feel cold or hot—but just right.