Its sort of like astral projection. It would be better described as an out of body experience, which tends to occur when we are sleeping.
However, when we are "spacey" or "zone out" frequently especially if we daydream or feel like we are living a dream, the conscious mind takes a bit of a trip outside of our bodies. We don't realize this, but it is happening. When you meditate you are becoming more aware of yourself, which is what you are observing.
If this happens a lot it is a sign that you are not grounded well enough. You can be quite the klutz when not grounded which can cause "dumb" injuries and mistakes. It can make it hard to focus, cause poor memory, and make it difficult to absorb knowledge. This is because your conscious mind is wandering off, or as my grandmother used to say "in the meadow" when it needs to be piloting your body!
But in your case I don't think you're grounded very well. It isn't bad to float away when meditating, but the point of meditation is to ground and center in your own mind so that you can function better. Then to clear the mind and focus. So you may want to practice grounding when you begin to see yourself. You'll feel so much better for the rest of the day if you do! =)