Meanwhile, who had that brief sense of your actual self?

I imagine you've heard of the "law of set and setting". I think it applies a whole lot to what you're describing. Basically, you're going to respond very differently to the same experience depending on how you're "holding" it: as a problem or symptom, for example; or as some sort of spiritual attainment; or as just what happens to be so for you at the moment.

If you'd sought out the experiences that you're describing by means of some meditation technique or even drugs, for instance, you could be saying, "Wow, this is powerful stuff, look at what's coming up for me! I'm free of what I used to call my 'sense of self' and I'm even going through stages of child development! Wait till I tell my friends/guru about this!"

Alternatively you could be saying in the very same situation, "Omigod, what a lousy trip this is! I've lost my sense of self, I'm going through stages of child development, and I'm afraid my mind is falling apart!"

Personally, I've done best moving through weird spaces when I've managed to let go of where I thought I was supposed to be, and just kept noticing where I was -- pretty much the way Eckhart Tolle recommends, too.

You're identifying some of what you experience as "stages of child development". Let me suggest, though, that that just happens to be what you've chosen to call them. It's your experience and you can call it anything you choose (obviously ). One easy way to get into distress, though, is to decide that it has to mean something, whether good or bad. If what you experienced were different from what the textbook said children were supposed go through, that would not mean you were doing it wrong. If, on the other hand, you went through all the stages exactly the way the textbook said, that would not mean you were guaranteed to live happily ever after, starting immediately.