OP, you seem to be worried about him, so I'll put in my 2 cents.
I agree with the two who suggested epileptic fit, the main clue would be the violent shaking.
Also, epilepsy is triggered by many causes, but the main ones I think are loud music, flashing lights, and so on, so you could ask yourself if anything like that was present in the bar at the time.
Anyway, you two guys (and bar staff) were concerned, while the other 50 or so people were not, so I would relax a bit, because you did whatever you could do.
Finally, both the 1669 number poster is to be thanked, as well as the guy who mentioned Government Emergency Number.
Relax, it's over. Good on you for trying to help!