When we’re in REM sleep1, our eyes begin to move quickly behind the eyelids, our brainwaves speed up, our temperature fluctuates, and our muscle activity is suppressed. It’s also one (but not the only) sleep stage in which we dream. Since REM mimics wakefulness in certain ways, some scientists prefer to call it “active sleep.” The purpose of sleep—particularly, REM sleep—is not totally understood2, but researchers now think REM sleep may help humans: This means that it’s important to make sure you’re getting enough total sleep each night before you worry too much about time spent in REM vs. non-REM. With this in mind, researchers have found2 that the first stage of REM sleep typically starts about 60 to 90 minutes after we fall asleep, and it lasts around 10 minutes. As the night goes on, we phase in and out of REM cycles, and the time spent in each gets longer and longer. The last stage of REM can get up to an hour in length, so most of our REM time happens during the back half of our sleep. The amount of time we spend in REM will vary depending on our age, with babies typically spending more time in this sleep stage5 than older adults. But generally, Girardin Jean-Louis, Ph.D., professor of population health and psychiatry at New York University previously told mbg, “Healthy sleepers might spend approximately 20% of their sleep time in the REM sleep stage.” Given that most people need between seven and eight hours of sleep a night, that means around 90 minutes of REM sleep a night will be a sweet spot. But again, it depends on the person and their unique sleep needs. Signs that you’re not sleeping enough—and therefore, probably not spending enough time in REM—include problems concentrating and remembering6, poor mood6, low sex drive6, lack of energy6, food cravings6, weakened immune function6, trouble losing weight6, and balance issues6. “The epidemiology7 indicates that there’s an optimal amount of sleep—about seven hours, eight hours for most people—but people who sleep longer than that actually do worse than people who sleep less than that,” he notes. One reason could be that going against your body’s natural sleep-wake cycle—either by sleeping too much or too little—throws off your circadian rhythm, explains integrative medicine physician Dana Cohen, M.D. So if you spend your morning snoozing in REM during a time when your body increases levels of energizing hormones like cortisol, it could throw off your hormonal balance, which has downstream effects. Signs of oversleeping include headache upon waking8, trouble falling asleep when you need to, and mental fogginess. And regularly spending too much time asleep has been linked with an increased risk of all sorts of more serious health issues7. It’s important to remember that the best thing to do if you feel you’re oversleeping is not necessarily to sleep less but to sleep better. That is, focus on making sure that your routine is supportive of deep and restorative rest. Some changes that will give you the most bang for your sleep buck include going to bed and waking up at the same time every day, sticking to a relaxing pre-bed routine, and cutting back on alcohol, which has been shown to delay and disrupt REM sleep. Finally, taking a nightly sleep supplement may help you achieve deeper sleep so you can wake up feeling more refreshed during a time window that works for your body.* Emma received her B.A. in Environmental Science & Policy with a specialty in environmental communications from Duke University. In addition to penning over 1,000 mbg articles on topics from the water crisis in California to the rise of urban beekeeping, her work has appeared on Grist, Bloomberg News, Bustle, and Forbes. She’s spoken about the intersection of self-care and sustainability on podcasts and live events alongside environmental thought leaders like Marci Zaroff, Gay Browne, and Summer Rayne Oakes.
