"The bed is meant for one main thing: sleeping," says Raj Dasgupta, MD, a fellow of the American Academy of Sleep Medicine. "If you stay in bed, then it gives your mind the feeling that it's time to sleep and not start your day." Even worse, he says, is if you fall back asleep. If your "just 10 more minutes" turns into "oops, it's been an hour," then you're waking up from REM sleep instead of the lighter stages of sleep that you would've woken up from had you gotten out of bed the first time. Waking up from that deeper sleep can actually make you even more tired throughout the day than someone who got less shut-eye but woke up from a lighter stage of sleep. Bottom line: When you wake up, get up.