I suffer from a condition called sleep paralysis, have done for many years. It has presented itself in the way you describe on a number of occasions. I seem to get it more during times of stress, or if Im really exhausted. Its a frightening experience but I have learned to deal with it now. Google 'sleep paralysis' and check if you have had any of the other experiences described.
If you had an epileptic seizure, its most likely you would have lost control of your bladder also.