what illnesses have severe weakness as a symptom
Other, more severe causes of weakness include: 1  cancer. 2  stroke. 3  heart attack. 4  muscle or nerve injury. 5  diseases affecting the nerves or muscles.
Weakness may be temporary, but in some cases it is chronic or continuous. Common causes of weakness include: 1  influenza. 2  insomnia. 3  medication side effects (often seen with mild tranquilizers used to treat anxiety). 4  polymyositis (inflammatory muscle disease). 5  chemotherapy. 6  hepatitis A, B, C, D, and E. 7  blood loss.