Hi. I have a Border Collie girl who has recently developed symptoms after excessive excercise. She requires lots of exercise, and we run her to her favourite game with the tennis ball. Although after a short time and when she stops running, she staggers and becomes disorientated, and looses her footing. She pants heavily and takes some time to recouperate. This has only just started happening and was always fine prior. She is just over 2 and has no other symptoms really? Although I have noticed she has become more defensive towards the property lately? Otherwise she is a very calm, sweet and loving dog.
I am NOT familar with issues that plague the border collie, but in Labradors the EXACT same type of thing is a genetic disease called Excercise induced collapse or EIC, you can look it up for the labradors on a google search, you could also look and see if there is something similar that affects border collie, try Border collie breed clubs they have a list of genetic issues. A trip to vet is a good idea.
OK so I was curious myself and did a google search and EIC is actually showing itself in Border collies and they are doing research on it, so here is the link. Good luck with your dog, I hope this is not the issue but you could help future generations with the testing being done. www.wootube.net/2010/02/exercise-induced-collapse-in-border-collies/