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There are countless sleep hacks, supplements, and cozy pajamas that may elevate your sleep game, but that doesn’t mean falling—and staying—asleep is easy. That’s why when some people feel totally fine with only a few hours of sleep under their belt, they assume it’s good enough—but that’s not exactly the case.

Put simply, sleep is the maintenance system that keeps every organ functioning properly, says Andrea Matsumura, MD, a board-certified physician in internal and sleep medicine. “The seven-to-nine-hour recommendation comes from decades of research showing that adults who consistently sleep within this range have better long-term health outcomes, including lower rates of metabolic disease, cardiovascular disease, cognitive decline, and mood disorders,” she says.

Meet the experts: Andrea Matsumura, MD, is a board-certified physician in internal and sleep medicine. Angela Holliday-Bell, MD, is a board-certified physician and certified sleep specialist. Morgan Soffler, MD, is a board-certified sleep medicine specialist and assistant professor of medicine at New York Medical College.

But what if you get less than seven hours of sleep a night and don’t feel tired? Ahead, find out why that might be a bit problematic—and how to get your sleep back on track, per experts.

Why You Feel Okay Even Though You Haven’t Slept Much

Personal sleep needs are influenced by genetics, age, circadian rhythm, medical conditions, environment, lifestyle, and hormonal transitions like puberty, pregnancy, periods, and menopause, says Angela Holliday-Bell, MD, a board-certified physician and certified sleep specialist. But more often than not, people feel “fine” with little sleep simply because their brain has adapted to chronic sleep restriction. “Over time, your brain adjusts its expectation of what ‘normal’ feels like, so the fog and low mood that come with short sleep begin to feel baseline,” she adds.

When you’re perpetually short on sleep, your brain essentially recalibrates. “Even though you’re cognitively and physiologically impaired, you don’t necessarily feel tired, because over time, you lose the ability to accurately perceive your own impairment,” says Dr. Matsumura. In most cases, people don’t even realize how tired they really are until they start sleeping enough.

On top of that, adrenaline and momentum are likely carrying you. “Stress hormones and alertness pathways can create a temporary lift when you’re tired, so your body releases cortisol and adrenaline to keep you moving, which can make you feel more alert even though you’ve under-slept,” Dr. Holliday-Bell says. This hormonal boost can temporarily mask fatigue, but it’s not a long-lasting solution, because chronically elevated stress hormones increase inflammation, impair glucose metabolism (when your cells break down sugar to create energy), and strain the cardiovascular system, Dr. Matsumura adds.

It’s also worth noting that some people are just less affected by sleep loss because they have higher sleep efficiency, which is the percentage of time actually spent asleep while in bed, says Morgan Soffler, MD, a board-certified sleep medicine specialist and assistant professor of medicine at New York Medical College. So they fall into deep sleep more quickly and ultimately spend more time in the stages that do the heavy lifting for memory, learning, and recovery. They feel refreshed and recharged with fewer hours, while someone else might need more overall time in bed to get enough restorative sleep, she explains.

All that being said, feeling “fine” and not fatigued isn’t the same as functioning optimally, so it’s still very important to prioritize seven to nine hours of shuteye a night. “For most people, functioning on short sleep comes from habit, adrenaline, or a busy lifestyle that forces them to push through, but they don’t actually recognize the deficits” in the long-term, says Dr. Holliday-Bell. Speaking of…

What Can Happen When You Get Under Seven Hours

A night or two of poor sleep won’t harm you, but a chronic lack of sleep, which is defined as regularly getting less than six hours of sleep a night, can have serious long-term effects on your health, Dr. Soffler says. “When you consistently miss your sleep goal, your brain has trouble locking in memories, regulating emotions, and keeping attention steady,” she says. “The body ends up with higher stress hormones, increased inflammation, and more strain on the heart and metabolic system.”

Here’s a closer look at what happens to the brain and body when you don’t regularly hit your sleep goal:

Worsened Mental Health And Potential Mood Disorders

A lack of sleep affects your emotions, so aside from being tired, you’re also more likely to be irritable—two things that, over time, can lead to depression and anxiety, Dr. Soffler says. “You might not feel miserable every day, but your baseline mood slowly drifts downward,” she says. A review from the American Psychological Association in 2023 looked at studies on the relationship between sleep loss and emotion using 50 years of research. It found that sleep loss results in fewer positive emotions such as joy, happiness, and contentment, while simultaneously increasing anxiety symptoms like rapid heart rate and uncontrolled worrying.

Cognitive Impairment

When you’re sleep deprived, neurological pathways slow down, causing reduced reaction times and a weakened state of mind, per 2023 research in Neurosciences. As a result, this can trigger an impairment in attentiveness, working memory, alertness, judgement, and decision-making in the short- and long-term.

Weakened Immune Function

Sleep is when your body heals and regenerates, and those who repeatedly sleep less than six hours a night are more susceptible to colds, flu, and infections, Dr. Matsumura says. “Regularly dipping below six hours significantly impairs the immune system in a way that’s consistently detectable in research,” she explains. A lack of sleep impairs immune function and promotes chronic inflammation, which weakens your body’s defense and increases disease risk, per 2021 research in Communications Biology.

Increased Risk Of Chronic Illness

Getting less than six hours of sleep on the regular disrupts hormonal balance, elevates blood pressure, and raises inflammation in the body, all of which may up your risk of chronic illness such as heart disease, diabetes, obesity, and even cancer, Dr. Matsumura says. Research supports this: A 2024 study in Nature Medicine looked at sleep patterns and the risk of chronic disease in nearly 7,000 participants over 2.5 to 6.5 years. It found that poor sleep is associated with an increased risk of all-cause mortality and cases of chronic disease development.

In other words, when sleep suffers, every part of you suffers. The good news: Even if your sleep is a mess right now, you can improve it. “Many of the effects of sleep deprivation are at least partially reversible once adequate, consistent sleep is restored, and cognitive function, mood regulation, and immune response often begin to improve within days to weeks of better sleep,” Dr. Matsumura says. “Hormonal balance and metabolic health may take longer, sometimes several weeks to months, depending on how long the sleep deprivation has been going on, but it’s possible to get your body back on track.”

**How To Score Solid, Quality Zzz’s: **Dr. Holliday-Bell recommends cutting off caffeine in the early afternoon, curating a regular wind-down ritual, and creating a cool, quiet, dark sleep environment to help your body settle into sound rest.

Another pro tip: Wake up at the same time every day. “Going to bed earlier doesn’t automatically mean you’ll fall asleep earlier, but waking up at the same time every day helps regulate your internal clock and makes it easier to fall asleep the following night,” Dr. Matsumura says. “I also encourage people to stop trying to ‘force sleep,’ so if you’re awake in bed for more than 20 minutes, getting up briefly and doing something calm in low light can actually help retrain your brain to associate the bed with sleep, not frustration.”

Remember: Sleep is restorative, so you’ll notice the greatest boost in energy, mental clarity, and overall well-being when the right amount of sleep is paired with conditions that actually allow your body to recover.

Andi Breitowich is a Chicago-based writer and graduate student at Northwestern Medill. She’s a mass consumer of social media and cares about women’s rights, holistic wellness, and non-stigmatizing reproductive care. As a former collegiate pole vaulter, she has a love for all things fitness and is currently obsessed with Peloton Tread workouts and hot yoga.