If nothing worse comes from the Hillary camp that has come before, this is probably his plan for the next three weeks. It's unlikely he can ever build himself back up, so he has to do everything he can to tear her down. Maybe he's hoping to land a shot on something like he did when he was going on about Hillary being sick, and use that to say, "See, see?! You can totally trust me on everything I say!"
Of course if he doesn't land any shots, he's just going to look desperate, and any claim he makes is probably going to be looked at with increasing skepticism.
My guess: a cursory look on google indicates that some research shows that steroids help with pneumonia (though it's far from conclusive). It could be he's hoping that someone discovers steroid medication is being used, and then use that to say she's taking PEDs. Nevermind that if even true, there are some steroid medications that are designed to help with any sort of issue, though he's probably betting on most people not knowing that.