Here's a question

Every so often I go on a binge of re-reading my own fics. And almost every time, I end up thinking the same thing: "These are pretty good. But...did I really write these??" In other words, it feels like I'm reading someone else's work. It's a little unnerving. I can't quite figure it out.

So, for those of you who write fanfic, do you go back and re-read your own old stories? How often? Is there a particular concatenation of circumstances that causes you to do so? How does it make you feel when you do? How do you find that you react to them -- do they feel like your own work or someone else's?

Now, for those of you who also write original fic: same questions.