Dr. Charles Lapp, a fibromyalgia and ME/CFS researcher, once told me that people with FM would do better to think of exercise as movement, as opposed to an hour of intense exercise.  For some, walking to the mailbox may be all the “exercise” they can handle at first.  But the important thing is to move.  Inactivity, whether it is lying down or sitting, will actually increase your FM pain.  During the day, it's essential to move frequently – even if it's just to walk to another room and back.