Many different illnesses and mental health conditions can cause fatigue and drowsiness, also known as lethargy. Medications, extreme physical exertion, and sleep disruptions are also common causes, as are lifestyle factors, such as a poor diet. While most causes of lethargy are not dangerous, it can sometimes indicate a severe illness, so experts often recommend seeing a health care professional if exhaustion lasts for several weeks.
Medical Causes
Drowsiness and fatigue can be the result of many chronic or temporary medical conditions. Thyroid problems, such as hypothyroidism, can slow the metabolism and may result in exhaustion or weakness. Organ disorders, like jaundice, are also associated with lethargy. Common illnesses, such as a cold, food poisoning, or the flu, can also result in days or weeks of feeling run down and tired as the body puts its energy into fighting off the infection.
Some serious illnesses can also cause a person to feel drowsy, weak, or unable to function normally. Addison's disease, in which the adrenal glands cannot produce enough hormones for normal body functions, causes chronic exhaustion. Meningitis, a dangerous infection, may also cause extreme drowsiness. Many heart conditions, including heart failure, are associated with a feeling of fatigue and muscle weakness. Since most serious illnesses cause multiple symptoms, lethargy that occurs with a fever, shortness of breath, severe neck pain, or fainting spells should be reported to a medical professional.
Treating Medical Causes
Curing lethargy caused by illness is usually a matter of diagnosing and treating the underlying cause. If fatigue is due to a common illness, it will typically pass in a few weeks. More serious conditions may need to be treated with medication or hormone therapy. Some causes of fatigue are very hard to treat, and patients may need to make lifestyle changes in order to manage the conditions effectively.
Psychological Factors
When psychological disorders are involved, lethargy may be accompanied by feelings of indifference or detachment, as well as exhaustion. For some people, the symptoms come and go, while others experience constant drowsiness or mental fatigue. The condition is often related to depression or bipolar disorder. In acute cases, it may also be a symptom of shock.
Some doctors believe that lethargy can also be caused by a combination of hormonal and psychological changes, like those that happen during menopause or postpartum depression. It may also occur during times of severe stress, such as during a divorce or following a death. If feelings of exhaustion or indifference last for a long time, or are accompanied by depression or suicidal thoughts, a person may want to speak with a mental health professional.
Treating Psychological Causes
Psychological causes of fatigue or indifference can be treated in a variety of ways, depending on the specific cause. Some type of psychotherapy may be helpful, as can making behavioral changes, but this might not be enough on its own. A health care professional may prescribe medications that can correct chemical imbalances in the brain if this is believed to be part of the cause.
Drug-Related Causes
Many medications cause drowsiness or fatigue as a side-effect, including antidepressants, antihistamines, heart medications, and many other prescription and over-the-counter drugs. In some cases, combining certain drugs can also cause symptoms. Many heart medication cocktails, such as digoxin and the complementary drug quinidine, frequently have this effect.
Taking recreational drugs may also cause lethargy. Drinking too much alcohol causes dehydration, which results in exhaustion and weakness until fluids and minerals are replaced. Mood-altering drugs, such as marijuana, slow down the central nervous system, causing extreme fatigue. Regular and excessive drug or alcohol use can turn these temporary effects of intoxication into chronic conditions.
Dealing with Drug-Related Causes
Speaking with a health care professional may be a good idea if persistent fatigue seems related to the medication a patient is taking. The symptoms may fade after the initial weeks of treatment, as the body begins adapts to a drug. Other times, the medical professional may switch the patient to a different type of treatment. Unfortunately, this is not always possible, and patients in these situations may need to consider changing work schedules, getting more rest, and finding other ways to cope with the fatigue.
Lifestyle Causes
Leading an unhealthy lifestyle can cause acute or chronic bouts of drowsiness. Lack of sleep naturally results in tiredness and mental exhaustion, and eating a low-calorie diet, or one that does not provide the body with enough nutrients, may also bring fatigue. Exercising too much or too hard can lead to dehydration and sudden drops in blood sugar, followed by extreme exhaustion and weakness.
Some temporary symptoms may be caused by sudden changes to a daily routine. Jet lag, for instance, sometimes disturbs a person's sleep. People who live in regions that observe daylight-saving time may also experience tiredness when the clock shifts forward or back. Luckily, these symptoms often fade after a day or two, as the body adjusts to its new schedule.
Treating Lifestyle Causes
Most lifestyle-induced causes are treated by stopping the behavior that is causing the problem. This might mean setting aside time for a nap each day, eating better, or quitting alcohol and drugs. Treating these problems early is important, since they can lead to many health issues beyond lethargy.
