Loss of conciousness can be mistaken for seizure activity, esp. when you're on drugs that increase the amount of electrical signalling going on.
I know that at the very least, to a layman, loss of conciousness due to a vasovagal attack was and can be misinterpreted as a "seizure". Happened to me and was not pleasant, the attending doctors didn't see the need for me to be rushed to the ER and set the people I was with straight.
I would imagine "white-out" loss-of-conciousness dosages of psychedelics could easily produce comatose or pseudoseizure states. The best thing to do in this case is keep the person from harming themselves or others (i.e. knocking things off shelves, falling) and remain calm. There's nothing worse than regaining conciousness to a flurry of people screaming about seizures and 911.