Something similar happened to me, sometimes to the extent that it became rather painful to take a deep breath again.
I had to go to a speech therapist a few years ago (I'd lost my voice thanks to a cold, and it didn't really come back). She was particularly keen on teaching "low breathing," meaning breathing from the diaphragm, as opposed to this shallow "upper chest" breathing. She said babies and small children don't have this problem, they breathe naturally, but it develops as you get older. It seems to be correlated with the sedentary occupation of using a computer, but I don't remember it happening when I was reading, only during computer use.