An important part of STD transmission is the sexual part. While that is a germy area, falling into a toilet is not going to result in std/herpes transmission. I wouldn't worry about this and take a nice shower and wash up. You should be fine.
GuitarRox is right - there is absolutely no risk for STDs, including HIV, from this. Most die quickly once exposed to air, and some require direct genital skin-to-skin (or mouth to genital) contact to transmit.
Unless you had some kind of sexual activity at this party, you aren't at risk for any STDs.