Why You Get Tired and Sleepy When You’re Sick

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Research shows that feeling sleepy when you’re sick could be an essential survival mechanism.

While the necessity and benefits of sleeping are still being investigated, scientists do know that sleep is the body’s way of taking time to rest, repair itself and heal. In studies of parasitic roundworms, scientists discovered a genetic mutation that caused worms that were exposed to stress to release a chemical that signaled their tiny brains to fall asleep.

Similar studies were also done on fruit flies. The results of those studies showed that the flies that slept when they were exposed to bacteria had a better chance of surviving than those who carried on with their normal, daily activities.

We’ve all been sick at one time or another, so most of us can attest to the desire to do nothing but nap when we’re not feeling well. But what causes us to get sleepy when we’re sick?

Reasons Why You’re Sleepy When Sick

Everyone knows that getting enough shuteye is a vital part of being healthy. Sleep is necessary for both the mind and body. It allows the body downtime to restore cells and repair tissue; and it works to help the brain consolidate memories, process information and learn.

illlustration of a woman strugling with allergy symptoms

When people miss out on sleep, they may face multiple health challenges, both physical and mental. However, the fact that being sick makes us want to sleep even more than usual is a puzzle that scientists are looking to solve.

The current theory supports that we feel extra sleepy as a way to force us to slow down and allow the body to do its job of healing. The majority of healing and restoration takes place in the deep phases of sleep, called slow-wave sleep or SWS.

But it’s not just forcing us to slow down that makes the body heal itself. There are several automatic responses and immune defenses that get deployed during the sleeping process. As your body forces you to slow down, it performs the following functions:

  1. Encoding: recognizing the foreign bacteria or virus and preparing for battle.

  2. Consolidation: gathering information and consolidating information about the foreign invaders.

  3. Recall: filing this experience away in case this same bacteria or virus returns. The recall is what makes people resistant to getting sick from viruses like chickenpox multiple times.

These processes can all occur while we’re awake; however, sleeping enhances the performance and effectiveness of these three steps. That’s why our body signals us to slow down and veg on the couch during a sick day rather than hit the town and binge on sangria.

How Sleeping Fights Sickness

Less Resting Energy Expenditure

When the body is fighting off foreign invaders, it needs as much energy as possible. If you’re out gallivanting, then it provides an extra challenge for the immune system to gather the resources it needs to help you heal. The more energy you conserve when you are sick, the more resources your immune system has to help you recover faster.

Blood Flow Diverted to Healing Process

Digestion, exercise, thinking, and moving all require blood flow. Your body needs that blood flow to send energy and nutrients to the immune system cells to fight attacks.

Less Exposure to External Influences

Our innate survival mechanism tells us that it’s dangerous to go out and hunt or gather when we’re not feeling well. In a weakened state, we’re more vulnerable, and we are less likely to get hurt or make a mistake when we stay home and rest when sick.

Endogenous Steroid Activity Reduced

Endogenous steroids are produced in the adrenal glands, and they naturally suppress the immune system and decrease inflammation. In ordinary circumstances, we want these working at full capacity, but when we’re ill, an inflammatory response signals the immune system to do its job. Therefore, since bedtime reduces the activity of these steroids, it helps expedite the healing process.

Endogenous Opioids Enhanced

The most famous endogenous opioid is endorphin, and both sleeping and moderate exercise help increase this level, which is why you’ve probably heard of people feeling better after a workout. However, resting is vital for health because these boost antibody and immune response.

Antioxidant Generation

Sleeping increases levels of alpha-lipoic acid (ALA), which is an antioxidant that promotes healing. Antioxidants help neutralize foreign invaders to keep us healthy.

Frequently Asked Questions

Can you oversleep when you’re sick?

You should feel free to rest as much as your body needs. Often, people tend to sleep the most during the first couple of days of feeling sick. As long as you wake up to hydrate periodically, and listen to your body's needs, we think you’ll be perfectly okay.

What sleeping position is best for cold sufferers?

People with a cold should make sure their head and nasal passages are elevated. Back and side sleeping are both suitable positions. We recommend propping your head up with a wedge pillow to provide a more natural angle. You could potentially rest your head on a mountain of pillows, but this could do damage to your neck, especially if you lie this way for multiple days in a row.

Learn More: How to Sleep With a Cold


Sometimes we want to battle our body and power through. We’re tough and invincible, right? However, when you’re fighting an infection, one of the best things you can do to speed the healing process is to get plenty of sleep and listen to your body when it’s telling you to slow down.

Jill Zwarensteyn

Jill Zwarensteyn


About Author

Jill Zwarensteyn is the Editor for Sleep Advisor and a Certified Sleep Science Coach. She is enthusiastic about providing helpful and engaging information on all things sleep and wellness.

Combination Sleeper

Sleep Advisor