What happened during this treatment?

I started ect awhile ago and each session has been more or less the same, go under wake up leave, no real problems. The other day it seemed like it took longer to go under but eventually it happened. I woke back up in my room but couldn't really remember much, just was unusually exauhsted and couldn't keep my eyes open. I closed them and then felt like I entered a state of sleep but was still conscious.I couldn't really move my body except for being able to shake a bit and felt like I was suffocating. I was freaking out and couldn't open my eyes, talk, or move so I just tried to shake was much as possible. this got the attention of my dad who called the nurses. I don't really remember much after that other than 3 nurses surrounding me but they kept me around for an extra 45 min before letting me go. since then it's never happened again and I don't really know what to make of it and I haven't gotten any decent answers from the nurses or doctors I asked