I, too, have cervical problems that cause a lot of pain. I notice that when my pain meds begin to wear off and just before the onset of severe pain, I get extremely fatigued. I don't know if it is the pending onset of pain that causes the fatigue or some physiological problem associated with the cervical problems. Maybe it is like a defense mechanism of the body that tries to get me off my feet when the bad pain is coming. Or maybe my mind just wants to check out before the pain gets bad.