Dehydration is an under-recognized leading cause of fatigue. Many people don't drink water at all during the day; instead they drink soda, energy drinks and coffee, all of which can cause even further dehydration. Dehydration not only causes fatigue, but a variety of negative side effects including: -Joint pain -Dry skin -Muscle cramps -Bloating -High blood pressure -Build up of toxins in the body -Weight gain Dehydration is the sole reason may people experience fatigue. Luckily this is an easy one to fix; drink a minimum of 8 glasses of water a day to avoid dehydration. I know I'm guilty of forgetting the WATER. When I get really down with the fatigue that's when I remember and start pouring the water down.