Not exactly sure what you're asking, but I'll try to help if I can.
I'm assuming this fish has been in the tank for some time. Are the other fish okay? What are your water parameters, what's in the tank? Any changes lately? Maintenance routine? Does the clown 'host' anything?
Did you see anything happen, or did you just notice that the fish is acting abnormally? I'm wondering if s/he was stung by something, or caught/beat up by another fish, maybe got stuck on a pump intake or in the rockwork? Have any other fish been harassing it lately?
We need as much information as you can provide. The more you tell us, the more likely you are to get an answer.
