[OT]Question for combat veterans

I was just reading "Major" by Rick Shelley and came upon a 
section where he talks about "combat sleep."  You dream and
go through normal phases of sleep but are still catalogueing
what is going on around you.  Is this true?

The reason I ask is I _always_ sleep like this unless I am
exhausted.  When I was younger I would tell people I wasn't
ever asleep because I could replay the last 10 minutes or
so of conversation in a room where I was.  I still wake up
every 40-50 minutes now and any odd sound in the house wakes
me up.	It's a good thing I go to sleep just as quickly.