I wouldn't say that is something to worry about, but I wouldn't say it isn't. At some point in our lives, we all start to forget things, or "space things out" as I would prefer to put it. I have done things like this, myself, usually when I am tired, lacking sleep, and coming down with something. One day, I drove half way home from work, without remembering doing it, and when I "snapped out of it" I wasn't sure where I was. I know that when my brain is over loaded with stuff and I have allot on my mind, (worried about things) my brain will shut down. Make sure you are getting enough sleep and take a good vitamin. Just keep an eye on things, but don't driver yourself nuts with it, either. Good luck and keep us informed!
I think if it is a one time incident it may not be too unusual. If it happens again or keeps happening I would see a neurologist.
take care,
mkh9