There are ways to get around that pre-cert, if you didn't stay over 24 hours for example you just stayed overnight, but was discharged before you hit 24 hours the hospital should bill it as a 24 hour observation stay, which is considered outpatient. Something I would definitely do, is contact the financial department at the hospital and see what they can do to get it fixed. I still would not lose sleep over it, it just may take a little work to get it taken care of. Perhaps if you fight it enough the hospital will just write it off or a portion of it anyhow.