Mind drifting

Do you ever find yourself zoning out into your own thoughts? Especially, when you're in a conversation with someone? Well, I found myself in that zone today. To be honest I can't even remember what I was thinking about, I just remember my mind wondering from one thought to the next. Did the person across from me realize that I was nodding my head and saying uh huh and oh reallys, even though I had only heard a word or two? K, maybe it was a few more words then that. Half way through the conversation I found myself realizing that I wasn't listening and I should be, because I actually did care what this person was saying. Is this "mind-drifting" another way of multi-tasking? Mind-tasking? How is it that our minds can focus on more than one thing at a time? The human body never fails to amuse me. I'm always learning something new about us human beings. This "mind-drifting" really has me thinking. Lots of unanswered questions. I think I might do some more research on this matter just to find out if this is a common thing that occurs to people and if so, why. Does this sort of "mind-drifting" happens to you? Do share.