Sometimes I am suddenly overcome by extreme fatigue and weakness. I feel as though my body weighs a ton and I can hardly drag myself across the floor. This usually happens after exercising or at the end of my work day. But sometimes this occurs in the middle of the day for no apparent reason. This can last for hours or sometimes an entire day. I do not have a stressful or strenuous job, and my exercise routine is mild at best. What could be the cause? I am overweight and have high blood pressure and cholesterol, although the blood pressure and cholesterol are under control. My blood sugar has been checked during these episodes, but it is not too low--it's usually in the 80's.