Hi Hopefull,
I do that a LOT. I've had lots of people tell me its a stess-coping mechanism or "dissociating" (Not as in DID, but "zoning out" as you put it!)
I'm glad you've found a way to lessen the amount of time zoning out. I've found that (since most of my stress is caused by other people) that getting away from them, even for 10 minutes can help. Listening to music or multi-tasking (as in not really paying a whole bunch of attention to whats stressing me) helps as well.
I find it annoying as well. And embarassing too, someone ALWAYS has to make a comment about it!