Tired all the time? You might need more than a cat nap—it could actually be fatigue. Here’s what to know.

By Elizabeth Yuko
July 12, 2021
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When people return to work after a vacation, there's a good chance they'll hear one comment multiple times throughout the day: "You look so well-rested!" Whether or not that's actually the case (have you tried traveling with kids and/or a partner who constantly complains?), it's become our go-to response to someone who's recently taken some time off. 

And there's good reason for this: According to the National Sleep Foundation's 2020 "Sleep in America Poll," 72 percent of us feel sleepy at least two days out of the week (excluding the pockets of time right before going to bed and after waking up), and 40 percent of adults surveyed said that this persistent tiredness gets in the way of their daily activities. In other words, feeling tired seems to be our default mode, so when we appear (or at least should appear) well-rested, people notice.

But why, exactly, are we so tired all the time—and at what point should you worry, if at all? As it turns out, it doesn't always only come down to needing to sleep a few more hours each night: There are several medical, circumstantial and environmental factors that can cause different degrees of fatigue that can seriously affect your well-being. Here are some of the most common explanations for why you're always tired, along with a few smart solutions to help you reclaim your rest.

The Difference Between Sleepiness and Fatigue

When describing feelings of tiredness, we tend to use the terms "sleepiness" and "fatigue" interchangeably, but Alex Dimitriu, M.D., double board-certified in psychiatry and sleep medicine and the founder of Menlo Park Psychiatry & Sleep Medicine, stresses that these are actually two different things. "Definitions are important, and splitting the hair between 'fatigue' and 'sleepiness' is essential, and something I do every day in my work as a psychiatrist and sleep specialist," he says.

Sleepiness, Dr. Dimitriu explains, "is the easy one," noting that "people who are sleepy would often say they could fall asleep or take a nap at some time during the day." Problems with both the quality and quantity of a person's sleep lead to sleepiness. 

Fatigue, on the other hand, is something else entirely. "People with fatigue may have low energy or low motivation, but they would not necessarily be able to fall asleep if allowed to do so," says Dr. Dimitriu.

Along the same lines, Chun Tang, MRCGP/DFFP, a general practitioner with Pall Mall Medical in the United Kingdom, points out that while feeling tired after a bad night's sleep or a long week at work is usually no cause for concern, if you feel exhausted the majority of the time, it could be a sign of fatigue. "Whereas tiredness generally subsides following a peaceful sleep or rest, fatigue is an overwhelming and prolonged feeling of exhaustion that does not improve after sleeping," Dr. Tang explains. Here's what to know about some of the potential causes for feeling tired or fatigued all the time.

Common Causes of Fatigue

The first step to dealing with constant or chronic exhaustion is to determine what's behind it. "Fatigue is a symptom with a very wide range of causes," says Katherine Green, M.D., director of the Sleep Center at UCHealth. "The challenge with fatigue is that each underlying cause has its own treatment." These include a variety of medical conditions, as well as certain circumstances and/or environmental factors.

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1 Physical Health Conditions

While Dr. Green specifies that sleep apnea is the most common medical cause of fatigue, she points out that there are many others, including insomnia, thyroid dysfunction and vitamin deficiency. According to Julia Blank, M.D., family medicine physician at Providence Saint John's Health Center in Santa Monica, Calif., additional physical health issues that can lead to fatigue include:

  • Anemia — either related to diet (like low iron or B12 intake), or blood loss (e.g. heavy menstrual periods or ulcers) 
  • Conditions resulting in malabsorption of nutrients (e.g. celiac disease, inflammatory bowel disease like ulcerative colitis or Crohn's disease) 
  • Endocrine disorders, which can disrupt hormones that regulate important bodily functions (e.g. thyroid disease, diabetes, Cushing's disease, hyperparathyroidism) 
  • Autoimmune disorders (e.g. rheumatoid arthritis, lupus) 
  • Pregnancy 
  • Side effects of certain medications, including antidepressants, anxiety medication, muscle relaxants, sleep medications, some blood pressure medications, antihistamines and certain cancer medications 
  • Heart disease (e.g., coronary artery disease, congestive heart failure, certain arrhythmias) 
  • Lung conditions (e.g. COPD or emphysema, where oxygen delivery from the lungs is impaired and there is increased effort needed for the lungs to continue supplying sufficient oxygen to the body) 
  • Infections like mononucleosis, flu and COVID-19, as well as chronic infections like HIV and chronic hepatitis
  • Being overweight 
  • Chronic pain 

RELATED: 11 Healthy Habits That Can Actually Help You Sleep Better

2 Mental Health Conditions

People living with mental health conditions experience different types of fatigue, Dr. Dimitriu explains. "I often describe a spectrum between 'sleep' and 'wake' to my patients," he says. "Depressed and sleepy people are on one end, [and] anxious people [are] on the other—essentially, too awake and often unable to sleep."

Along with fatigue, depression can be accompanied by low energy and lack of motivation. While tired people will have an interest in doing things, but lack the energy, those who live with depression often won't have the interest in the first place, Dr. Dimitriu explains, noting that if you experience any thoughts of suicide, you should seek medical care and evaluation immediately and/or call the National Suicide Prevention Lifeline (1-800-273-8255). 

In contrast, Dr. Dimitriu says that people with anxiety, ADHD, and, more rarely, bipolar disorder, often report feeling "tired but wired"—which, he says, is what it sounds like: having low energy and motivation, but being too "wired" to get enough sleep, or fall into a deep sleep. 

RELATED: Set Your Alarm One Hour Earlier to Reduce Your Risk of Depression, Sleep Study Suggests

3 Circumstantial and/or Environmental Conditions

Not all fatigue is caused by a medical condition: There are also a number of other factors and circumstances that can leave you feeling tired all the time. "Fatigue can often be circumstantial and related to stress at work, long-distance travel, or unhealthy lifestyle choices such as poor diet, smoking, and binge-drinking," Dr. Tang explains. "A restful environment is also important for good sleep hygiene. A sleeping environment that is too loud, too bright, or simply uncomfortable, can result in regular sleep disruptions and fatigue." (Even if you're in bed for the recommended seven to nine hours, you may not be clocking enough quality sleep during that time; sleep quality is as crucial to overall health and daily functioning as sleep quantity.) To help narrow down the potential causes of your extreme exhaustion, he recommends trying to identify the daily stressors that could be contributing to it.

RELATED: The Real (and Very Normal) Reason You're So Exhausted After Therapy 

What to Do If You Feel Tired All the Time

Once you've figured out why you're constantly fatigued, it's time to take action. If there's a medical reason for your persistent tiredness, you'll need to work with your doctor to treat the underlying issues.

"For sleep apnea, identifying the problem with a sleep study will be necessary to treat the issue, and treatments range from CPAP machines to mouth guards that you sleep with at night, to surgeries," Dr. Green explains. "For underlying medical causes like thyroid dysfunction or vitamin/hormone deficiencies, blood work will identify those causes and allow for medical treatment. The same is true for anxiety, depression, SAD, and migraines: all have specific medical interventions which will very effectively improve the symptom of fatigue, but it is important to properly identify the cause of the fatigue."

If stress is the root cause of your fatigue, Dr. Tang recommends tackling the sources of your stress—which frequently involves our jobs. "In today's fast paced society, people often feel under pressure to work long hours and undertake unrealistic workloads," he explains.  "Setting boundaries for your work schedule and allotting time to relax and unwind before bed can promote a more restorative, restful sleep."

And while you're on your quest to find out what's making you tired all the time, don't forget about all the top tips for improving sleep quality, like sticking to a sleep schedule, making the time for some type of exercise, and eating a healthy diet, Dr. Blank adds.

When to See Your Doctor

Given the variety of symptoms associated with fatigue and the range of potential causes, Dr. Blank says that it's a good idea to seek medical advice if your fatigue lasts for more than a couple weeks. Alternatively, if you experience any of what she calls "red flag symptoms" along with that nagging tiredness—like chest pain, shortness of breath, persistent fever, night sweats, and/or unexplained weight loss—discuss them with your doctor right away.

Ultimately, the sooner you're able to pinpoint the cause of your fatigue, the sooner you'll be able to take the steps necessary to feel better. "Successful treatment of fatigue is going to be dependent on properly identifying the underlying reason, and the first step is talking to your doctor," Dr. Green says. "If you are getting the right amount of sleep (at least 7 hours), paying attention to sleep hygiene, and still feeling exhausted in spite of those things, then it's definitely time to talk to your doctor to figure out what is going on."