Is my betta sick? Please help!?

I got a Betta fish yesterday, his name is Conrad, and I changed his water this morning, and now he's face down in his rocks, heavily using his gills, sometimes he'll swim around all panicked and then go back down to the bottom. Then, after a while of this, he'll go back to the top and float around (not really swim) and then the process will start over again. Is he sick? I really don't know. I got him from Petco (It was the Build-A-Betta Weekend). He's in a 1/2 gallon bowl, in treated tap water (I got a sample of the water treatment drops) with a gravel and a fake plant.