I've experienced the same to some extent. For example--maybe not the best example, but nonetheless--I've went to the bathroom knowing I've locked the door, but soon realized it hasn't been locked. Stumped as I get, the only reasonable explanation to me would be false memories.

When you continuously do a task over and over (lock the door, for example), you will of course expect that you've done it this time, too. When you don't do it, and you come to realize the absence of this task having been done, you get a false memory... That's my non-medical idea of what's bringing this about.

I think in your case it may have been something a bit more serious than my example, though.