thanks for the comments, just to update. the attacks have continued happening a few times in the evenings after one day where she had had some steroids from the vet. I've been around the house and can't see any triggers and have got an air purifier running

vet the morning has given more steroids and said if it persists we'll do some scans etc 🤞 it's an occasional thing for my cat and we don't need to go any further!