In RBD, sleepers thrash around violently and shout as they dream.
And chocolate has been found to trigger it off in people who already suffer from it, making bedtime worse for RBD sufferers.
The choccie scientists have been able to prove this by studying people in special sleep labs.
Usually people are naturally paralysed when they dream in a process called "atonia". This is the body's way of preventing injury when asleep.
But the scientists found caffeine in chocolate blocks atonia which means the sleeper can act out their nightmares.
The scientists say if you don't already have the disorder there is no need to give away your choccies!