Why Am I So Tired? The Many Causes of Fatigue

What is fatigue?

One of the most common complaints that I hear when taking a history from a patient of a current illness is that the patient says, almost as an afterthought "... and I don't know why I am so tired." In most instances, this complaint is not the main reason that the patient is seeing me. In some instances, "being tired" is mentioned to physicians during a routine checkup after the patient said they have no current health concerns. So, should I as a physician treat the comment like an afterthought and concentrate on the "real reason" the patient is being seen? I could focus on the "real reason" for the visit, but if I skip asking questions about "being tired," I may miss finding out information or clues about the patient's illness and completely overlook a potential diagnosis and treatment for the patient.

Therefore, the first thing to understand about "tired" is what the patient means by the word. Does the patient mean they feel sleepy or fatigued -- they are not the same. Fatigued (tired) describes a lack of energy and motivation, not feeling sleepy (although both can occur together). If the answer is fatigue, the next step is to determine if the fatigue is mental, physical, or both. Now we are beginning to narrow down some clues to the cause of the fatigue, but we (the patient and the doctor) still have a long way to go together.

What causes fatigue?

Fatigue is mainly a symptom and not a disease in itself. The key is for the doctor, with the patient's help, to discover the underlying cause of fatigue. The patient's input is important because accurate answers to the doctor's questions may lead the doctor toward a diagnosis or, at least, may suggest what medical tests may help provide a diagnosis. For example:

  • If the patient says things like "Starting any project is tiring...It is exhausting to get motivated... Concentration takes all of my energy....or... it takes so much effort just to feel normal," the fatigue may have a mental cause.
  • If the patient says things like "I'm exhausted after walking up a flight of stairs...I lose muscle strength after simple repetitive movements..., or I had a viral infection but now I seem unable to get my normal strength back," the fatigue may have a physical cause.

However, there are reasons that are "normal" for a person to be tired. Normal people who have intense physical or mental challenges can become fatigued. If the intense activity is halted (for example, "Whew! The exam is over"... or... "I had to really run to catch Fluffy after her leash broke"), the fatigue gradually dissipates over hours or a day. When patients describe longer-lasting fatigue or fatigue with otherwise normal activity, then it may be telling the patient and their doctor there is an underlying cause of their tiredness.

Fatigue as a symptom of underlying conditions

So what are some common questions you may hear your doctor ask that gives clues to the underlying causes of fatigue? The first set of questions may lead to some frequently seen causes of fatigue:

  • Are you possibly pregnant?
  • Have you started a new exercise or diet program?
  • Does any recent work change like extended hours or night shifts?
  • Any new stress (death of a family member, teenager rebellion, work pressures, divorce, financial problems)?
  • Are you taking any new medications?
  • Do you get tired at certain times (during or after your period, after interactions with a certain person, or after taking medicine)?
  • Any use of illegal or un-prescribed drugs, herbal products, or other supplements?

The answers can give the patient and their doctor some insight into three major categories of problems that can have fatigue as a symptom:

  1. sleep problems,
  2. mental health, and
  3. medications.

In addition, such questions can provide insight into short-term normal fatigue such as bereavement, exercise, or changes in normal activity.

Testing and further diagnosis for fatigue

The other types of questions are a bit harder for both the patient and the doctor to use as clues because if the patient responds positively, often the physician will need some additional testing is done (possibly by other doctors or tests with results that will not be immediately available to your physician) to uncover or clarify an answer. If you have a primary physician, that doctor should already have most of these questions partly or fully answered. However, the primary care doctor may not have these answers if you see multiple physicians, have not seen your doctor "...in quite a while..." or you are seeing a physician for the first appointment. Examples of such questions include:

Answers to these questions can lead to clues and further tests for underlying causes of fatigue that stem from:

These diseases listed between parentheses are only a few examples of the major categories of diseases and other fatigue problems that can stem from underlying diseases such as cancer, autoimmune diseases, and even therapy such as chemotherapy and radiation therapy.


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What is the prognosis for fatigue-causing disorders?

I find that most (unfortunately, not all) underlying causes of fatigue can be identified when the patient and I make a good effort to uncover the clues that lead to discovering the underlying cause of their fatigue. Treatment of fatigue is based on the treatment of the underlying cause, but that's another long story. Consequently, the answer to the person who asks "Why am I so tired?" is given when the underlying cause(s) is identified, usually done with you answering the tough questions accurately and the diligence in pursuing clues by your doctor.

Art and science are forever changing; in general diagnostic methods and how doctors use them often enhance patient care. However, many times our patients and we doctors don't think of the cumulative effects of lifestyle, minor changes in health, medication effects, and aging on one's overall health; we focus on a specific symptom and assume a single cause ant treatment. Functional medicine, a relatively new way to approach diagnosis and treatments may offer methods and treatments that are designed for each individual patient by identifying multiple causes that contribute to the problem and then trying multiple treatments to reduce or cure the problem. Chronic problems like fatigue, inflammation, and others may be solved or maximally reduced by the approach.

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Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care


The Institute for Functional Medicine. What is Functional Medicine?

UpToDate.com. Approach to the adult patient with fatigue.