Brief periods of generalized weakness are common, especially after a strenuous workout or a stressful emotional situation, and usually they just mean that you have overexerted yourself. Generalized weakness is not a cause for concern as long as you are able to move all parts of your body and complete your normal daily activities, even if you have to work a little harder to get things done.

Weakness that does not have an obvious cause, such as overexertion or a viral or bacterial illness, or that does not get better or go away is more of a concern.

Sudden, severe generalized muscle weakness may be caused by a serious problem, such as coronary artery disease or heart failure. Weakness that is quickly getting worse may be caused by a nervous system problem, such as a transient ischemic attack (TIA) or stroke, or a poisoning, such as botulism. Muscle weakness that comes on suddenly or is getting progressively worse requires a visit to a doctor.

On rare occasions, generalized muscle weakness is caused by another health problem, such as:

• Cancer, such as lung cancer, leukemia, or lymphoma.
• Problems with the thyroid gland, which regulates the way the body uses energy.
  • A low thyroid level (hypothyroidism) can cause fatigue, weakness, lethargy, weight gain, depression, memory problems, constipation, dry skin, intolerance to cold, coarse and thinning hair, brittle nails, or a yellowish tint to the skin.
  • A high thyroid level (hyperthyroidism) can cause fatigue, weight loss, increased heart rate, intolerance to heat, sweating, irritability, anxiety, muscle weakness, and thyroid enlargement.
• Guillain-Barré syndrome, a rare nerve disorder that causes muscle weakness in the legs, arms, and other muscles and that can progress to complete paralysis.
• Myasthenia gravis, a rare, chronic disorder that causes weakness and rapid muscle fatigue.
• A problem with the minerals (electrolytes) found naturally in the body, such as low levels of potassium or sodium.

See your doctor if your generalized weakness is so severe that you cannot complete your normal daily activities.