This COULD be an epileptic seizure, but most unconscious forms involve a period of stiffness, rather than becoming immediately floppy. I can think of other causes for this, such as a mild stroke, poisoning etc. As he hasn't done this again for such a long time, it's probably not worth treating. A stroke may explain the sleepiness, however, but I've no experience with them. Was he normally mobile when he'd recovered the sense of where he was etc, or was he limping?