I'm a little concerned

Last night I was eating dinner with a friend and apparently missed 5 minutes of conversation...as in, no memory, pick up the record stylus, skip 5 minutes ahead, and put it back down. There was a different song playing in the background, I didn't respond to a question as I should have--I was answering one from a long time before in the conversation. I've defensively dissociated to some degree most of my life. That's why, for example, I don't have much memory of my childhood or my memories of things jumble. But this was much worse. The thing that disturbed me about this is that I have absolutely no memory, just missed time, and usually I'm aware of myself and may seem 'outside' my body or otherwise watching a scene or remember being there but not necessarily what was done or said, but not checked out entirely. I had absence seizures as a very small child, and I suppose it could be something like that, except for the length of time and the fact that I apparently kept time with the music and said, 'uh-huh' at appropriate times rather than spacing out completely. I've had really small times this has happened, once standing waiting for a light to change and missing the entire green light, once driving where I fortunately wasn't alone and someone dragged me back to consciousness as I was about to cross into another lane, but that's pretty much it. It's really rare, and the thing is, these things don't happen when I'm emotionally uncomfortable, like true dissociation, but rather without an apparent trigger, other than MAYBE something rhythmic (music, the wheels on the roadway, the lights). I'm definitely going to ask my psychiatrist what she thinks it is, though. Whereas usually I come back to myself with out a sense of suddeness, this was like *bam*, at first you don't realise anything's different, and then you realise your environment has changed completely. It's very disconcerting. Maybe it's something physical rather than psychological...I just don't know, and it really scared me.