Betta is having problems swimming, he seems to be staying at the top and resting there somewhat sideways HELP?

My Betta (Mozart) was doing fine earlier in the day. I was about to feed him but the water looked dirty so i changed it. I keep the water temp between 70 and 80 and feed him brine shrimp and betta food flakes. I feed him after i changed the water and he ate just fine but right now he is having problems swimming to the bottom of the bowl. I find him resting at the top in a somewhat sideways angle. Is my betta dying?