It's 3 a.m., and you need to get up at 5 a.m. for your flight or your work shift or your conference. The clock is forcing you to make a decision: Curl up in bed for two hours of shut-eye or power through the next day? While your instinct and your drooping eyelids may urge you to take a nap, this might make you feel even worse than if you hadn't slept at all, says Michael A. Grandner, PhD, research associate at the Center for Sleep and Circadian Neurobiology at the University of Pennsylvania. "If you get less than 4 hours, there's a good chance that you'll wake up in slow-wave sleep, which can leave you disoriented, irrational and extremely irritable," Grandner says—in other words, like a hot mess. He explains that our bodies are pretty resilient and can function reasonably well without sleep once in a while, so you'll be able to chug through the day even if your mind will be a little fuzzy (this means catching a plane wouldn't be a problem, but driving a car would).
Best advice: Fire up the coffee pot, stay busy until your natural circadian rhythm kicks in and then hang in there until your normal bedtime.