It's hard to say whether it was a seizure or not, but I can say from experience that my brain activity is more apparent right as I'm starting to fall asleep. My epileptologist told me that 'popping' as you are falling asleep is normal, everyone does it. It is just more apparent in people with seizures, I wouldn't worry about
it too much. Until it starts to effect your waking life, it's possible that it's normal brain activity. I hope that's the case!