Everyone feels tired now and then. Sometimes you may just want to stay in bed. But, after a good night's sleep, most people feel refreshed and ready to face a new day. If you continue to feel tired for weeks, it's time to see your doctor. He or she may be able to help you find out what's causing your fatigue and recommend ways to relieve it.
Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include
One disorder that causes extreme fatigue is chronic fatigue syndrome (CFS). This fatigue is not the kind of tired feeling that goes away after you rest. Instead, it lasts a long time and limits your ability to do ordinary daily activities.
NIH: National Institute on Aging