11 Causes of Sudden Extreme Fatigue or Exhaustion

You know what fatigue feels like. You might feel low. Or tired. Or a bit mopey. You might want to lay down and chill for a bit on the couch. But what causes extreme fatigue, like when you feel as if you're weighed down by bags of sand? Or it's too hard to get out of bed?

As a symptom, fatigue is a tough one. "Fatigue is defined as tiredness, exhaustion or lack of energy precipitated by exertion or a stress. It's a subjective symptom and, unfortunately, we don't have objective measures on an exam, making fatigue one of the easiest or most difficult diagnoses I see during the say," Andrew Patane, MD, internal medicine doctor with NYU Langone Health, tells LIVESTRONG.com.

If you see your doctor for fatigue, be prepared to answer a lot of questions. Dr. Patane might ask a patient how long they've had the fatigue, what brought it on and what other signs and symptoms they're experiencing (fevers, night sweats, weight loss, sleep disturbances). How you answer will guide the doc in deciding what diagnostic tests they might run.

Lifestyle factors, medications and medical conditions can all cause extreme fatigue. Here's are some things that may be going on below the surface.

Sudden overwhelming fatigue could be a sign of a viral or bacterial infection.

Examples of viral infections that often cause tiredness, according to the Cleveland Clinic and Mayo Clinic, include:

• Flu
• COVID-19
• Mononucleosis (mono)
• HIV

Fever is common with all of these illnesses, but other signs and symptoms vary. For example, a severe sore throat might suggest mono, while the loss of taste or smell likely signals COVID-19.

Sudden severe fatigue can also accompany serious bacterial infections, according to the Sepsis Alliance. Examples of these types of infections are:

• Urinary tract infection (including bladder and kidney infections)
• Bacterial pneumonia
• Dental abscesses
• Sinus infection

In addition to fever, most bacterial infections cause fever, chills and pain or discomfort in the affected area.

A vitamin deficiency, such as not getting enough vitamin D or vitamin B12, could cause you to feel severely tired, per the Cleveland Clinic. Dehydration can have the same effect.

You could also feel suddenly exhausted if you've recently started a high-protein diet. It's not the protein itself making you tired, but the lack of carbohydrates. Severely restricting carbs causes your body to enter ketosis, where it breaks down fat for energy, per the Mayo Clinic. The side effects of ketosis (sometimes called "keto flu") include fatigue as well as headache, weakness and bad breath.

These side effects are usually temporary, but if ketosis is causing your sudden energy crash, you may want to add more fiber-rich, complex carbohydrates to your diet, such as fruits, vegetables and whole grains like oatmeal and brown rice. The Dietary Guidelines for Americans recommend carbs make up 45 to 65 percent of your total daily calories.

Similarly, skipping meals or following a very low-calorie diet could sap your energy. Keep in mind that people assigned female at birth (AFAB) should avoid eating fewer than 1,200 calories per day, and people assigned male at birth (AMAB) should eat at least 1,500 calories per day, according to Harvard Health Publishing.

But keep in mind that the 2020-2025 Dietary Guidelines for Americans recommend adult people AFAB eat somewhere between 1,600 and 2,400 calories a day, and people AMAB get 2,000 to 3,000 calories daily, depending on age and activity level. Check the guidelines' chart of estimated calorie needs, or use a calorie counting app.

This is one of the first areas Dr. Patane evaluates when he sees patients for fatigue. He may ask them if they are:

• Drinking more alcohol than usual
• Having extremes of activity (such as training for an endurance race or undereating for their exercise level)
• Working more than usual
• Doing night shift work
• Having a work-life imbalance
• Practicing poor sleep habits

While some of these might sound obvious, it sometimes takes the help of a professional to point these out and guide you in making the right changes.

Medications may be designed to make you feel better, but starting a new prescription often comes with unintended consequences, and one of those side effects can be fatigue.

Some meds that can cause extreme fatigue, according to Dr. Patane, include:

• Antidepressants
• Antihistamines
• Beta blockers for blood pressure
• Benzodiazepines for anxiety

If you've recently started a new medication, talk to your doctor. They may be able to change your prescription or alter the dose to treat you while minimizing these side effects.

Mental health issues are known for dragging down your energy. "These can all present with fatigue," Dr. Patane says.

Stress is also a key component of fatigue. A build-up of stress over time (without a proper release or self-care measures) can leave you feeling emotionally exhausted, and thus, severely tired, per the Mayo Clinic Health System.

While you may be on the lookout for chest pain to signal problems with your heart, you should also add sudden-onset fatigue to the list, per the American Heart Association. (Other accompanying symptoms of a heart attack include dizziness, lightheadedness and pressure in the upper back, per the AHA).

In addition, the AHA points out that fatigue or confusion can be one of the initial symptoms of a stroke. Other signs might include a severe headache, arm weakness and difficulty with walking or talking.

While there are more than 100 conditions considered autoimmune (fibromyalgia, multiple sclerosis, ulcerative colitis, type 1 diabetes and lupus are just a few), according to the Autoimmune Association, at their heart, it's the immune system attacking the body that causes them.

Fatigue is the most commonly reported symptom across these diseases, and sometimes the sudden episodes of extreme fatigue can be profound and debilitating. The reason? High levels of inflammation contribute to the kind of tiredness that can make carrying out everyday tasks difficult.

These conditions can be tricky to receive a diagnosis for, in part because symptoms, like fatigue, can be so non-specific. They do tend to run in families, though, so be sure to tell your doctor about your family health history.

Iron-deficiency anemia is defined as not having enough iron in your body, according to the National Heart, Lung, and Blood Institute. And fatigue is the most frequent symptom.

The condition can cause sudden lethargy and is more common in people who menstruate, those who eat vegetarian or vegan diets and endurance athletes.

Your doctor can diagnose you based on a physical exam and blood tests, and they may recommend iron supplements or diet changes to get your stores — and your energy — back up.

Postural orthostatic tachycardia syndrome (POTS) is a group of symptoms that occur when your blood doesn't circulate properly, according to Johns Hopkins Medicine. Doctors don't totally understand the condition or why it happens, but they know that when a person with POTS stands upright, more blood collects in their lower body, causing the heart to beat faster to pump blood up to the brain.

Some people with POTS describe it as having sudden fatigue attacks, while others say it's like having waves of sudden extreme fatigue and nausea or extreme fatigue "out of nowhere." It can present differently depending on the person, but other symptoms might include:

• Feeling lightheaded or dizzy when standing, or fainting
• Nausea and vomiting
• Brain fog
• Muscle cramps or muscle pain
• Headaches
• Feeling shaky
• Sweating a lot

POTS tends to run in families, and there's a link between POTS and having highly mobile joints (Ehlers-Danlos Syndrome), per Johns Hopkins Medicine. If you think you have it, see your doctor, who can run a test and make a diagnosis.

We mentioned that fatigue can be tricky to nail down, and the same goes for chronic fatigue syndrome (CFS), also known as myalgic encephalomyelitis or systemic exertion intolerance disease. The hallmark symptom of CFS is profound fatigue that lasts at least six months, doesn't go away with rest and can't be explained by an underlying medical condition. While it's a long-term condition, it could come on suddenly.

The exact causes of CFS aren't known, but in some cases it's thought to develop after someone's been infected with a virus, such as the novel coronavirus. In fact, according to estimates by the COVID-19 Symptom Study, up to 15 percent of people who get COVID will develop post-viral chronic fatigue syndrome, or "long COVID."

Other symptoms of CFS, according to the National Health Service, include:

• Headaches
• Trouble sleeping
• Joint or muscle pain
• Sore throat
• Trouble concentrating or forgetfulness
• Feeling dizzy
• Fast or irregular heartbeat

When there's something wrong, it can be hard not to think about the worst-case scenario. So it's important to get checked out by your doctor before making any assumptions. But when you're telling your doctor about your symptoms, they will think about if there's any reason to suspect cancer.

Some red flags (which do not point to a diagnosis, only the possibility of additional testing), include fatigue that's accompanied by fevers or night sweats, unintended weight loss or lumps and bumps under armpits and the side of the neck, Dr. Patane says. If you have any of these, you should see your doctor sooner rather than later, he adds.

If your fatigue prevents you from engaging in work or school, social or personal activities, then you should see your doctor, Dr. Patane says.

"When in doubt, it never hurts to speak to your doctor about this. It can be a simple evaluation, and we may be able to say there's nothing seriously wrong and suggest lifestyle modifications," he says. "One of the best ways to get better from fatigue is with good sleep hygiene and by slowly increasing daily exercise."