My doctors told me that CRPS/RSD aside, anyone with high level chronic pain experience the brain actually re-wrires itself so to speak. Maybe the brain re-wires itself so it considers almost constant pain signals are NORMAL. I don't know.
Falling asleep that mimics narcoleptic events and/or symptoms, would be good enough for me to get whatever proper tests need to be done, in order to RULE OUT or diagnose you properly.
Also, what type of meds are you taking? Do you drive? Have you fallen asleep while eating, drinking, walking, climbing, sitting or standing, getting up from a chair or couch...etc, you know what I mean.
Lastly, I get sleepy often from battling pain combined with a semi-sedentary lifestyle these days, your RSD pain is enough to deal with, so get yourself to your doctor and he/she will advise you the next step, best of luck and I really hope you wind up okay.