I read in a book (will search for it and quote it's name) that the breathing activity of the brain may get very weird when meditating. Breathing can get slow, and a practitioner of 40 years even wrote that sometimes his breathing would completely stop for several minutes!
So I think it is a good sign. I predict that this won't continue for long, your body will get used to your meditation routine and will adjust accordingly. Please keep us posted.