When people have a hard time sleeping, or waking up, or staying awake during the day, often it's because their natural circadian rhythms have gotten off-kilter. But new technologies - including special masks, glasses, heart sensors and apps - are trying to remedy that.
Circadian rhythms guide the body through the 24-hour cycle. They tell us when it's time to eat and sleep, and when it's time to get up and start a new day.