poor clown fish

[FishBulbHead]

i just bought a clown fish on wednesday and then today he wouldnt swim much and then he started swimming weird on his side like and the he kinda died. I was wondering if anyone knew what was going on, what to do next and if my other fish is at risk, also a clown fish. I did do a pretty suffient water change after the little guy died.

 

Thank you in advance