Account being hacked?

[SummerSnowLeopard]

Okay, can I have some advice on something please? On Facebook, my friend got a message from "me" saying I hate her. And then, on my own website, I apparently send a message about a school dance to some unknown person. So, if I end up "saying" something that's either rude or "off", please let me know about it. I have no idea what's going on but I'd appreciate some advice.