The sooner you are able to extract your kid from this crazy arrangement of being locked in a basement bedroom with an active alcoholic who's having seizures ... the more time your child will have to live a normal child's life. If your ex is away at rehab, use the time to interview lawyer after lawyer until you find a strategy for bringing unsupervised visits to an end. You do have a strong case.
After one of my ex's drunken antics (can't even remember which one now), I got a court order varying our divorce order such that he would have supervised visits with Kid with a third party agreeable to both of us who would keep Kid in direct line of sight the entire time, plus SoberLink testing before/during/after visits. I didn't try to end his access to Kid altogether because I wasn't sure that a judge would order that, even though ex was clearly unwell. Instead I tried to make it as awkward and uncomfortable as possible, so he wouldn't want to exercise his access. It worked, sort of - he raged and threw fits and dragged me to court over and over, but he gradually saw less and less of Kid. (And then he died, which is a whole other story). So strategically - there's a lot of room to maneuver between "child is locked in bedroom with wet-brain" and "Mom prevents child from seeing Dad".
(FWIW - the make-it-super-awkward strategy was also used by a friend in a nasty divorce in which the father was suspected of abusing the child. She couldn't completely cut the father off until he was formally charged [he has since been charged and his trial is scheduled], so she made the visiting arrangements as awful as possible for him [he had to sit in his ex-in-law's living room being glared at by ex-mom-in-law while attempting to play like a normal parent with the child]. It worked - the visits became less and less frequent and eventually stopped).