There are a few reasons you are feeling tired without any reason. One of them is anemia, which is a lack of red blood cells and conversely, oxygen from the lungs is not properly brought to the tissues and cells. Anemia may be caused by deficiency of vitamins or minerals, internal bleeding or chronic diseases. Women who are at “that time” of the month are susceptible to anemia as blood is lost during menstruation. Still, iron deficiency due to menstruation is less than in pregnant women or lactating mothers, as their body needs extra iron to maintain healthy blood levels. Things may also go wrong when your thyroid glands refuse to cooperate with you. Thyroid hormones, thyroxine (T4) and triiodothyronine (T3) are responsible for metabolic processes in the body. Too much thyroid hormone causes hyperthyroidism which speeds up metabolism while too little thyroid hormone slows down metabolism. Hyperthyroidism causes fatigue and muscle weakness and starts in the thighs. Doing energy demanding activities become difficult and other symptoms include weight loss, feeling warm, shorter menstruations, increased heart rate and thirst. Hypothyroidism also causes fatigue and muscle weakness. The symptoms are reversed to hyperthyroidism such as weight gain, feeling cold and longer menstruations. Diabetes, notorious for causing a range of problems in the body, is also related to fatigue. As glucose is the staple fuel of the body, it is not utilized properly in patients with type 2 diabetes as the absence of insulin causes the glucose to build up in the body. Without its staple fuel, the tissues of the body are not nourished properly and causes fatigue. Sadly, being sad can also be the reason you feel tired. Depression induces negative feelings and also has negative effects on the body as it causes a reduction in energy levels, changes in sleep and eating patterns, decreased concentration and overall laziness and worthlessness which keeps you in bed all day.