Here's my experience with something similar.

I was dehydrated from drinking booze throughout the day and not drinking enough (or likely any) water. Later in the day I smoked and I could feel something was off. My vision started fading out (think like when you wake up and everything fades in but the opposite) and before I knew it I was unconscious.

Apparently I smashed my fucking face when I fell over and it triggered seizure. I woke up from one not knowing what happened, someone told me I was about to have another, and sure as shit I did. The second time around I actually experienced some strange visual/auditory sensation where as the first one I just kind of felt like I rapidly fell asleep.

Point of the story is, if you bash your head when you pass out it can trigger a seizure. I forget what it's called but it's possible.

If you have residual effects consult a medical professional