Two periods!?

If this bleeding was just spotting, I would take a pregnancy test to be sure that it wasn't implantation bleeding as the previous poster said. However, if you're not pregnant, one out of the ordinary period isn't uncommon. If you're on a hormonal method bleeding between periods is a common side effect. If you experience it again, however, consult a doctor as abnormal bleeding can be a symptom of things like endometriosis that should be dealt with as quickly as possible so that the treatment is the least invasive as possible.