I wouldn't want to be flying - even in F - when suffering from unresolved food poisoning and all the implications of that if it's not fully resolved.
Being unfit to fly covers all sorts of medical conditions and ailments and not flying is for the protection of others as much as the individual.
I've read enough threads on FT about flights where people have been ill causing discomfort to others because the pax threw up in the cabin pr messed up a toilet for example and that dosen't even cover the flights that needed to be diverted.