My fish is dying

Question
I changed my fish's water and now he is starting to tilt! I don't know what went wrong (his bowl looked clean when I started).He is using his left fin to prevent himself from turning over, but he's still flipping over.I think this is the end.

Answer
I don't have much information to go by. What kind of fish? How large is the bowl? A gallon? What temperature is the water? Did you use tap water  dechlorinator? Did you make sure the temperature of the new water was as close as possible to the temperature of the water you changed out?
Use something to reduce his stress for the moment, anything that adds slime coats will help. Make sure he has the correct temperature, and do some research on your specific fish to be sure that a bowl is an adequate size for his species. If it is anything other than a betta, then the answer is no - a bowl is not big enough.