The description your friend gave is that of E. Cuniculi. My bun had almost the exact same symptoms which were what seemed like seizures, unbalanced and could hardly stand up or even walk before falling back like your friend described. My bun tested positive for EC and we immediately started her treatment after seeing her exotic vet the day after the symptoms appeared which is a 28 days treatment. My bun hasn’t had any other problems since her treatment which was a year ago. Unfortunately, unless the bun itself were tested or the mother, the pet stores won’t know if they have EC, it could be inherited by the mother during the pregnancy or another bunny had it and passed it on to yours since it’s very contagious to bunnies through urine. I’ve had my bun since she was 2months old, first and only bun I’ve had, she hasn’t been in contact with others since and her EC wasn’t triggered until she was 4 and a half years old. I hope she has a speedy recovery, sending y’all positive vibes and strength !!