May not be anything to do with hips. Congestive heart failure can manifest itself as a cough and fainting i.e. the dog collapses but gets back up again and carries on. Had a Jack Russell who suddenly started to show these signs when she got to about 15 years old. The vet told me that dogs only use a small percentage of their heart capacity but as age catches up on them they can quickly go from being very fit and agile to failing as their heart capacity has finally got to the stage where it can't keep up. Vet gave me some pills to try but told me the old dogs heart was dying quicker than the rest of the dog. While the little terrier didn't seem in any pain I imagine suffering from bouts of unable to get enough oxygen in to keep up with an active body was no fun and the pills didn't help so sadly I put her down.