Ever had such a crummy night of sleep that you wake up feeling more tired than you were the night before? Whether you were tossing and turning for hours, found yourself unexpectedly staring at the ceiling before sunrise, or were tending to a cranky little one, you most likely got out of bed desperate for caffeine…and a nap.
While chronic sleep deprivation is widely known to increase the risk of serious health issues like heart disease, diabetes, and cognitive decline, research suggests that just one bad night can set off a chain reaction that disrupts nearly every system in your body. Of course, one bad night won’t send your general health into a tailspin, but it’s important to recognize that missing out on much-needed Zzzs has a very real—and very quick—impact on your body.
From messing with your hormones to clouding your brain, here’s exactly what happens in your body after one sleepless night—plus what you can do to recover.
- ABOUT OUR EXPERTS: Sunjya Schweig, M.D., is an integrative family physician and founder of the California Center for Functional Medicine. Alex Dimitriu, M.D., is a physician double board-certified in psychiatry and sleep medicine and founder of Menlo Park Psychiatry & Sleep Medicine.
1. Your Brain
In addition to feeling like a sloth, you may notice some pretty significant shifts in your mood and focus after an awful night of sleep. “Sleep is essential for processing memories, clearing out harmful waste, and keeping brain chemistry balanced,” explains Sunjya Schweig, M.D., an integrative family physician and founder of the California Center for Functional Medicine.
In particular, sleep loss disrupts key brain chemicals like dopamine, serotonin, and norepinephrine, which help regulate mood, motivation, and focus. “A drop in serotonin can leave you feeling anxious or down, while lower dopamine levels zap your motivation and make it harder to concentrate,” says Schweig. “On top of that, poor sleep causes a spike in adenosine—a chemical that builds up in the brain and makes you feel sluggish and foggy.” That’s why even the simplest tasks can feel exhausting after bad sleep.
Read More: How To Fight (And Fix) Persistent Brain Fog
Insufficient sleep also causes cortisol—the stress hormone—to go into overdrive, which keeps your body stuck in high-alert mode, making you feel more anxious, irritable, and generally on edge, according to Alex Dimitriu, M.D., a physician double board-certified in psychiatry and sleep medicine and founder of Menlo Park Psychiatry & Sleep Medicine. “Without proper rest, cognitive processes like memory, decision-making, and reaction time slow down, which explains why sleep-deprived individuals often struggle to focus, feel emotionally unstable, and experience increased sensitivity to stress,” he says.
2. Your immune system
Sleep is essential for keeping your immune system strong—and even one bad night can weaken your body’s defenses. Natural killer (NK) cells, which help fight off viruses and even cancer cells, decrease when you don’t get enough rest, making it harder for your body to stay protected, according to Schweig. “T cells, which play a key role in adaptive immunity, also don’t function as effectively after poor sleep,” he adds. “Normally, these cells become ‘stickier’ during sleep, allowing them to latch onto and attack harmful invaders, but when you’re sleep-deprived, they lose this ability, weakening your immune response.”
Sleep also helps the body regulate inflammation, and falling short influences levels of inflammatory markers like interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP)—all of which are linked to serious health issues like heart disease, neurodegenerative disorders, and autoimmune conditions.
3. Your testosterone levels
Your body’s hormonal balance depends on consistent quality sleep—and even one poor night can throw it off. One important chemical that’s heavily impacted: testosterone, which is crucial for energy, muscle recovery, mood stability, and brain function in both men and women, Dimitriu says. Since testosterone is primarily produced during deep sleep, “less deep sleep means less testosterone, leaving you feeling sluggish and unfocused,” says Schweig.
4. Your Appetite
As if the other hormonal impacts of screwy sleep weren’t enough, a not-so-restful night also impacts your hunger and satiety hormones in a way that transforms your appetite into a bit of a monster.
“Sleep deprivation disrupts the hormones that regulate hunger,” explains Schweig. “Leptin (which signals fullness) decreases, while ghrelin (which makes you feel hungry) increases.” This shift makes you crave high-calorie, sugary foods, setting the stage for energy peaks and valleys—and even greater mood instability—throughout the day.
Read More: Squash Your Sugar Cravings ASAP With These Dietitian Tips
Changes in insulin function also contribute to your sudden cravings and endless appetite. “Sleep is essential for regulating pancreatic function and insulin signaling,” explains Schweig. “After a night of poor sleep, your body becomes less sensitive to insulin, causing blood sugar levels to rise.”
The result? A temporary state of insulin resistance that can leave you feeling sluggish and craving carbs, he warns. Over time, chronic sleep deprivation can increase your risk of developing type 2 diabetes and other metabolic issues.
5. Your Clarity
If you’re feeling borderline incapable of working or otherwise performing at your best after an awful night’s sleep, it’s not all in your head. Studies show that sleep deprivation can impair performance as much as having a blood alcohol level of 0.08%—the legal limit for intoxication. “Lack of sleep slows reaction times, makes problem-solving harder, and clouds decision-making,” says Schweig. “It also stifles creativity by making it harder for the brain to connect new ideas, so sleep-deprived folks are more likely to make mistakes, have accidents, and miss work.” It’s not a pretty picture—and can become downright dangerous if it becomes a chronic issue.
6. Your muscle recovery
Since the body releases growth hormone, which is essential for repairing and rebuilding muscle tissue, during deep sleep, a night of poor sleep can hinder muscle recovery and growth significantly, according to Dimitriu. “Without enough deep sleep, muscle recovery slows down, making you more prone to soreness, fatigue, and even injury,” he says. “Sleep deprivation also increases cortisol, which can break down muscle proteins and hinder muscle growth.”
Another affront to your fitness routine: Lack of sleep also simply leaves you feeling less motivated and energized to get moving. Missing one day at the gym may not be a big deal, but it certainly doesn’t do your health and fitness goals any favors.
What to do After a Night of Bad Sleep
Sometimes, crummy sleep is completely unpredictable or unavoidable, so do yourself a favor and don’t add to the already-increased stress levels it causes! There’s plenty you can do throughout the day to help your body regain balance. A few priorities: Drink plenty of water, focus on eating lots of protein, do your best to resist faceplanting into sugar, get outside, and attempt a little light movement.
Otherwise, do your best to get back into a good sleep routine by avoiding screens and stimulants later in the day, enjoying a soothing evening ritual or two (like reading or taking a bath), and considering support from sleep-loving supplements like lemon balm and magnesium glycinate.
And, finally, be patient. “While extending sleep duration in the following nights may partially recover some cognitive and physiological impairments, studies indicate that sleep deprivation’s metabolic and inflammatory consequences can persist beyond the recovery period,” says Schweig. Your focus, memory, and decision-making may also take a couple of days to bounce back fully, he adds. Until then, do your best to get consistent sleep and stick to those helpful habits as much as possible.