I had something similar happen to me when I was 17. I was in hospital after a motorcycle accident and insisted I could shower myself but collapsed in the shower. The left side of my body was paralysed and I couldn't speak properly for 3-4 hours but then it went away and I was back to normal. I assumed it was a stroke but they said don't worry about it, you'll be fine and I was.
So it sounds totally plausible to me and he was also very lucky.
