We’ve all been there before: you promise yourself you’ll wait a few more minutes – and suddenly, it’s 2 a.m. and you’re still wide awake. Maybe you’re watching a new favorite Netflix episode or fretting about a morning meeting – whatever the underlying reason, you’ve been tossing and turning in bed all night instead of getting the shut-eye you so desperately need. What most of us don’t understand, however, is what happens to our bodies when we don’t get the optimal level of sleep, which for most adults is between seven and eight hours. Next, we asked a few doctors to explain how the body reacts to too little sleep – and their answers may surprise you.

Focusing on mental and physical tasks becomes more difficult.
According to Jan K. Carney, M.D., M.P.H., Ph.D., associate dean for public health and health policy at the University of Vermont Lana College of Medicine and the National Institutes of Health, sleep is critical to health every age. “When we don’t get enough sleep, it’s harder to stay alert, focus on school or work, and respond quickly while driving,” Dr. Carney says.

Your memory and mood are affected – and your appetite increases.
Sleep physician Dr. Abhinav Singh, MD, FAASM, medical director of the Indiana Sleep Center and a member of the Sleep Foundation Medical Review Panel, says believe it or not, losing valuable sleep time and excessive alcohol consumption can produce similar physical results. “Sleep deprivation is associated with impaired memory, depressed mood, increased appetite (think obesity and diabetes) and diminished responsiveness,” he says. “Increased reaction time, which some studies have compared to being worse than being drunk.”

Chronic sleep deprivation can lead to long-term physical and mental health problems.
While Dr. Carney says the short-term risks of sleep deprivation are things we’re all familiar with – feeling drowsy and having trouble concentrating – the real risk is what sleep deprivation can cause over time. “Chronic sleep deprivation is associated with an increased risk of chronic health conditions such as high blood pressure, heart disease, obesity, stroke and depression.”

You can’t make up for lost sleep.
Unfortunately, you can’t “catch up” on sleep – once those hours are gone, they’re gone forever. “It’s best to develop and maintain regular sleep habits over time,” shares Dr. Carney, adding that sleep deprivation doesn’t “learn to live” either. “The best way to ensure both adequate sleep and quality sleep is to develop good sleep habits.” That means implementing a routine with consistent bedtimes and wake-up times every day – even on weekends. “Regular exercise will help, as will avoiding caffeine or alcohol before bedtime,” Carney says. “Our environment is critical – we need a calm, quiet, dark and cool place to sleep on a regular basis.”