My sister has narcolepsy and cataplexy, narcoleptics tend to reach REM stage much quicker than those who don't have it. She is too afraid to try lucid draeming, because she thinks it may provoke her cataplexy (which is a dream like state that causes muscle paralysis and is very scary for those who it happens to.)
She knows when it's happening, but she can't really control it. Hope that sheds some light on this thread.

Happy Dreaming my friend.