Whats wrong with my beta??? URGENT?

I just got my beta a few hours ago from petsmart. He was fine and all and didn't seem to have any aparent problems. Now hes floating at the top of his new bowl and swimming in circles. However, he gets better all of a sudden and just swims normally. Then he slowly goes on his side and swims wierdly again. Then it goes back to normal. Whats wrong with im? I just got him and I dont wanna lose him! :( I used the water the lady gave me at Petsmart then I added clean water, not tap water. I added pebbles in but I made sure to rinse them first. Idk what to do! The lady said i didnt need to worry about him and that i could even add tap water for his new water when chanching it. Should i put him back in his little cup again and wait? Or does he have this bladder problem thingy? Cuz i didnt even feed him :O