I agree with krista on this one. If your body is trying to flush something out - let it. Immodium will work on diarrhea regardless of the cause because it extracts extra water out of the bowels and slows them down.
I don't really see how you could get food poisoning from parsley though? Unless I guess it was really really contaminated.
Stick to the BRAT diet - Bananas, Rice, Apples, Toast, in that order as can be tolerated. Definitely get some fluids with electrolytes. Pedialyte ice pops are pretty good when you feel ick. Other than that I usually drink fruit water because its got electrolytes but not all the sugar in a sports drink which can be irritating in and of itself.
ETA: As an IBS sufferer, I don't even take antidiarrheals unless absolutely necessary (i.e. i have to be somewhere!). I seem to feel better just letting my body do what it wants to, as long as I have the time to wait around until its decided its through..