I had a similar problem. Never got to the point of drifting off while driving. My doctor ordered up a sleep study. The first study I had, I did not get into REM sleep at all. So they repeated it and got me to sleep first (meaning they put the equipment on me first before other patients so I got to sleep first). So during that second sleep study I had one REM episode and it showed many episodes of sleep apnea. I went onto nasal cpap at night and had been good up until recent. Now I'm back to being terribly tired through the day. My NP prescribed some stimulant but I didn't try it b/c I didn't want to interfere with my crps meds.

To simplify, see if your doctor thinks a sleep study would be needed.