Why would my bow shoot to the right suddenly?

I have shot my Martin Prowler (rt. hand) every evening for the last several weeks. It has been spot on until today . It now shoots about 1 1/2" to the right of point of aim. I checked the trophy taker rest and my sights and it all feels solid as usual. The bow wasn't dropped or anything like that. Can anybody give an idea of what may cause this sudden shift of impact? Thanks for your thoughts in advance.