8 year old has breathing episodes

My boyfriends son is 8 and has downs. Sometimes (maybe once every few months) he has these episodes where he gets a really barky cough, which eventually leads to his throat closing. We use epinephrine (advised by doctor) and if he has another episode he goes to the hospital. These episodes only happen at night and often when he’s sick, but he has had a few when he wasn’t sick too. He’s still learning how to talk so he can’t really tell us how or what he’s feeling. His doctor said he suspects histamine overproduction but never did any tests. He gets sick easily and is usually congested, but that got fairly better after we started him on children’s claritin. I know a lot of health issues can come with having downs, so I was just wondering if this sounds familiar to anyone or if anyone had ideas on what I could tell his dad to ask a doctor about, like certain tests we should do or possible conditions to look into. If anyone could help I would greatly appreciate it.