Regarding Mohammed – this from Wikipedia:
“... Muhammad is reported to have had mysterious seizures at the moments of inspiration. According to Philip Schaff, during his revelations Muhammad, "sometimes growled like a camel, foamed at his mouth, and streamed with perspiration." Welch, a scholar of Islamic studies, in the Encyclopedia of Islam states that the graphic descriptions of Muhammad's condition at these moments may be regarded as genuine, since they are unlikely to have been invented by later Muslims...”
As stated above, the idea that muslims would have invented these 'seizure' stories does seem to be exceptionally unlikely. It would appear that the accounts of Mohammed foaming at the mouth, etc. are genuine.
It boils down to a very simple question of whether you believe that Mohammed was able to converse directly with God and that talking to God produced these physical effects on a mere mortal; or that Mohammed was just simply having epileptic seizures with the attendant religious delusions.
I know which one of those options I'd put my money on.
http://goo.gl/TZneY