Some causes of tiredness include anemia, diabetes, heart disease, sleep apnea and depression, as WebMD indicates. Menopause may cause hot flashes and night sweats that interfere with proper rest at night, resulting in daytime tiredness.
Anemia makes it difficult for the blood to circulate oxygen throughout the body. Iron deficiency is the most common type of anemia. Iron is important in the circulation of oxygen in the blood, and people with low iron have heart palpitations and feel dizzy when they stand, explains WebMD.
Although doctors do not know why diabetes makes people tired, a possible reason is that when changes in blood sugar levels occur, the body needs plenty of energy to deal with those changes, according to WebMD. A person experiencing extreme tiredness may be suffering from congestive heart failure. The condition occurs when the heart does not pump properly. A person with the condition feels more tired when he exercises.
Sleep apnea prevents the body from getting enough oxygen when the person sleeps. If a person lacks enough oxygen, he cannot get enough rest and may find himself feeling sleepy during the day. To sleep better, a person with sleep apnea can use a machine referred to as the continuous positive airway pressure, or CPAP, machine, says WebMD.
Depression lowers the energy levels of the body, and that makes a person feel tired. Also, a depressed person may find himself unable to sleep and waking up earlier than usual in the morning, explains WebMD.