depression
"I started taking this medication a couple of years ago when I was diagnosed with a chronic illness that seems to be putting me in pain every day.  I did not know if it was a side effect of the medication or my illness that gave me such horrible headaches (not quite a migraine, but pretty close).  I was off the medication for 4 weeks in that time--no headache; but the depression came back.  I got back on it.  The headaches are back now, I don't have energy, I have to take a nap everyday to function the rest of the day; and the chronic pain persists. "