To quote Dave Barry, I swear I am not making this up:
Exploding Head Syndrome is the occurrence of a brief hallucination at or near the onset of sleep, specifically, that of a flash of light, a loud noise, or, more vividly, the sensation that there has been an explosion in your head. It can be accompanied by a sense of disorientation or fear. Since people are often reluctant to report such a strange phenomenon to their doctor, it isn't known how prevalent the condition is, or what its neurological/psychiatric implications may be. A single study performed in 1989 suggest that it may be related to stress, caffeine and sugar intake and normal aging - and that it is probably fairly common.
Apparently, the only trauma associated with EHS syndrome is the fact that elderly individuals who experience it are often convinced that they are experiencing a stroke or are suffering from brain cancer.
Actually, this has happened to me several times, although I never worried about brain cancer or a stroke for that matter. I always thought it was the CIA or the space aliens trying to activate my sub-dural neuro-cortical control implant. Fools. I'd like to see them get through my Gaussian Scattering Helmet.