If you still feel ok 24 hours later, you probably don't have much to worry about. Typically, you will get cramping, sometimes severe, which feels similar to stomach flu, but fortunately does not last more than a day. On the other hand, if you ate a bowl of e-coli, you can be in some serious trouble.

Last time I had food poisoning, I got a bad case of cold sweats and passed out, and felt like hell all day.