You wake up in the morning, yet feel as if you’ve run a marathon in your sleep. Your limbs are heavy, your mind foggy. No, you didn’t pull an all-nighter, nor are you fighting off a physical illness. You’re most likely battling depression.

Anxiety, tiredness, and negative thoughts are seen as the symptomatic triad of depression. But even though depression is a psychological disorder, it can trigger somatic (physical) symptoms including loss of energy.

Often, this sense of constant exhaustion unleashes a vicious cycle that can maintain depression for years. Chronic tiredness, a physical disorder, is often confused with depression because the symptoms are so common. Each, however, can trigger the other, so it’s possible to develop both.

The bottom line is that the fatigue you experience during a depressive episode is not just in your head. It’s a physical sensation, deeply rooted in your body. But why does depression make you tired? Let’s delve into the science behind this.

Being depressed is tiresome

“My problems commenced when I had to leave University. I suffered from a flu-like condition, which led to panic attacks, depression and complete exhaustion for a couple of months,” wrote a user on a medical Reddit thread, whose identity I won’t divulge.

“I am taking mirtazapine which helps me get a full night’s sleep now, but I still lack the energy that I need to do things. When I do feel well enough to get out and about and do something with my day or go out for the evening it exhausts me and results in me needing to recover for a few days,” wrote another user.

Reports such as these are abundant all over the internet. They’re not even surprising given one in ten Americans are affected by depression at some point, and 80% of the clinically depressed are not receiving any kind of treatment.

“Some of my patients have been surprised and shocked when I’ve told them they were depressed,” says clinical psychologist Angel Adams. “They think it’s something else. If they have a lack of energy or fatigue, they might just think they’re doing too much. Sometimes they think, ‘It’s just this illness’ or ‘I had a break-up with somebody’, but really they’re experiencing depression as well as the illness or the grief reaction.”

Many of us simply don’t understand what depression looks like, the researcher stressed.

“People don’t quite understand that you can still function and have depression,” says Adams. “A lot of people think if you have depression you’re going to quit your job and so on, but many people continue to work, continue to function but to a very different degree. You don’t have to be suicidal to be depressed. You can just be clinically depressed and think, ‘This is the way my life is.’”

How depression affects both mind and body

Depression affects appetite and sleep — both vital to generating and replenishing energy. In most cases, patients report insomnia and getting less sleep, though sleeping too much will also ruin your mood and energy levels.

Even when patients with depression do get reasonable hours of sleep (seven hours is considered the bare minimum), most report waking up “unrefreshed” and tired throughout the day. That may be because people with clinical depression don’t get the same kind of quality sleep as everybody else.

Researchers who scanned the brains of the clinically depressed found:

• it takes much longer to fall asleep
• the total sleep time is reduced
• there is little or no deep sleep
• REM sleep occurs earlier in the night
• patients wake up more frequently during the night, which may last long enough for the person to be aware of these awakenings
• patients wake up earlier in the morning and can’t get back to sleep, even when they are very tired

Scientists assess the quality of sleep by measuring brain activity. Depending on the frequencies of the measured electrical signals, sleep can be divided into different stages.

A normal person will go from stage one to four when falling asleep, and then follow the reverse order when waking up. The fifth stage is called rapid eye movement sleep (REM) because the eyes move frantically — it is in this sleep stage that we dream.

Dreams are very important to our psychological well-being. Even when we have repetitive dreams of everyday occurrences, this helps the mind ‘put things in order.’ Here’s an enlightening account by sleep researcher Rosalind D. Cartwright, from the book The Twenty-four Hour Mind: The Role of Sleep and Dreaming in Our Emotional Lives (public library):

“The more severe the depression, the earlier the first REM begins. Sometimes it starts as early as 45 minutes into sleep. That means these sleepers’ first cycle of NREM sleep amounts to about half the usual length of time. This early REM displaces the initial deep sleep, which is not fully recovered later in the night.”

“This displacement of the first deep sleep is accompanied by an absence of the usual large outflow of growth hormone. The timing of the greatest release of human growth hormone (HGH) is in the first deep sleep cycle. The depressed have very little SWS [slow-wave sleep, Stages 3 and 4 of the sleep cycle] and no big pulse of HGH; and in addition to growth, HGH is related to physical repair. If we do not get enough deep sleep, our bodies take longer to heal and grow. The absence of the large spurt of HGH during the first deep sleep continues in many depressed patients even when they are no longer depressed (in remission).”

She continues, “The first REM sleep period not only begins too early in the night in people who are clinically depressed, it is also often abnormally long. Instead of the usual 10 minutes or so, this REM may last twice that. The eye movements too are abnormal — either too sparse or too dense. In fact, they are sometimes so frequent that they are called eye movement storms.”

There’s another pattern related to REM sleep in the depressed: they don’t remember what they dreamed or have a tough time recalling fragments. Thus, the mood-regulating function of dreaming may be disrupted in the depressed brain.

Depression fatigue may be rooted in stress

It’s not clear what causes depression, but prolonged stress seems to play a major role. When we’re stressed, the brain is flooded with the stress hormone cortisol. If stress remains heightened for a long time, there will be more cortisol and less dopamine and serotonin — low levels of these ‘happy chemicals’ have been linked with depression.

Each of these neurotransmitters plays a critical role in managing your mood and energy levels. Serotonin helps regulate your sleep cycle, appetite, and mood. Dopamine motivates you and gives you a sense of pleasure. Norepinephrine mobilizes your brain and body for action. When these neurotransmitters are imbalanced, your sleep quality suffers, your motivation plummets, and your energy levels drop dramatically.

Stress may exhaust the brain and lead to depression, which seems to trigger a vicious cycle: you’re depressed, so you become more stressed; you have trouble sleeping, so you feel tired; you feel tired so you don’t feel like doing anything meaningful anymore, which makes you more depressed. It really is terrible, and once the circle is complete, most people have a hard time breaking free.

This is why depression can be very cruel, and serious medical attention needs to be considered. Both depression and insomnia can be treated with antidepressants. Most antidepressants belong to the class called selective serotonin reuptake inhibitors (SSRIs), and insomniacs who start taking one of those drugs often find relief for their sleeping problems. However more than a third of patients with depression don’t respond to medication.

Sleep disruptions: more than just insomnia

Sleep disruptions are a common side effect of depression. And we’re not just talking about insomnia. You might also experience hypersomnia, or excessive sleepiness, which can leave you feeling groggy and lethargic during the day.

Sleep is the body’s time for rest and recovery. When your sleep cycle is disrupted, your body isn’t able to recharge effectively. As a result, you wake up feeling unrefreshed and fatigued, even if you’ve logged in a full night’s rest.

Non-pharmaceutical methods of addressing insomnia can help with depression. A few short tips that might help include:

• exercising during the day, but avoid doing so two hours before planning to go to bed,
• avoid caffeine (coffee, tea, energy drinks) and alcohol,
• use deep-breathing exercises to relieve anxiety.

Nutrition and depression: how they affect sleep

Depression can sometimes lead to a loss of appetite or a lack of interest in food. This can result in nutritional deficiencies that further exacerbate feelings of fatigue. Key nutrients such as iron, vitamin D, and B vitamins play a vital role in energy production. When your body is deficient in these nutrients, it has less fuel to run on, leading to increased tiredness.

So why does depression make you tired? It’s a complex interplay of stress, disrupted brain chemistry, sleep issues, physical symptoms, and nutritional deficiencies. These factors can all feed into each other, creating a cycle of depression and fatigue that can be hard to break.

Remember: feeling tired all the time isn’t solely confined to depression. In fact, a slew of physical disorders can cause these lethargic moods. Before visiting a psychiatrist, the best course of action is to first have basic blood tests. The doctor will then be able to check for infection, anemia, and thyroid problems, which could all be relevant.

Understanding the reasons behind the fatigue can provide a roadmap for managing it. Remember, if you’re struggling with depression, you’re not alone, and help is available. With the right support and treatment, you can manage your symptoms and regain your energy.