Of course, everyone feels tired often during the course of a normal day or week. It’s normal to be tired after a long day or after vigorous physical activity. But feeling very tired a lot of the time can be a symptom of many different diseases and conditions. Causes can range from lack of sleep and over-exercise to medical and surgical treatments. The lack of energy you feel when very tired can sometimes interfered with your normal daily activities, leading to problems with attentiveness and concentration.

Doctors consider fatigue, in medical terminology, to mean a reduced capacity for work or accomplishment following a period of mental or physical activity. For example, muscles fatigue if they are called upon to repetitively work for an extended period. Most of the causes of tiredness are also associated with fatigue. A person with tiredness or fatigue lacks energy, feels weary, and is constantly tired. Symptoms can include fever, body aches, and lightheadedness. These can be more serious, including fainting, palpitations, chest pain, difficulty breathing, or confusion.