Need help. One of my catch dogs doesn't catch anymore

Does he act like he is over heated...excessive panting and general delerium, with complete lack of strength. If so could be two different things. We have overheated some catch dogs before and they will never be right again if they passed the point of heat stroke but did not seize. Other could be one heck of a bad case of worms. Have seen bad cases cause complete loss of strengh in a dog that is only acting a little over normal activity. Also has he been cut badly before and how did he act? Unless he has just lost the heart its gonna be a medical condition caused by something that you will have to eliminate down to the cause.