This has happened to people before, back before the seal brought you I think. I switched out with a pretty unpleasant version of myself, Sam Winchester's alternate tried to kill half of Lawrence, and my boyfriend actually was killed by an alternate version of his genetic predecessor? person he was cloned from? older brother. The seal brought him back, but not until the real Clark had been back for about a week.
I know that's not going to help you feel less guilty, if that's what's going on with you right now, but just keep in mind that there are people around who have pretty much literally been there.