Hi, I had a similar experience with Tuppence who is 10 years old. It started a bout 6 weeks ago, exactly the same, not running about as much as usual (and she's normally like a 2 year old), wouldn't jump up and wouldn't go up or down the stairs. It coincided with yet another phantom pregnancy, so I assumed this was the cause, but from experience the symptons only last for about 10 days. Having sorted that side out and several trips to the vets to check there wasn't any other obvious cause, the conclusion was it must be joint problems, but like Barney, it all came on very quickly and there is no obvious signs of any pain. So my OH bought some joint support supplement tablets, the main ingredient being Glucosamine, with Chondroitin and Manganese and I started her on one a day last Saturday and, not wanting to tempt fate, she seems to be getting back to her normal self gradually. Might just be coincidence but I'm keeping my fingers crossed, as I was advised that it might take a couple of weeks for the tablets to build up in her system.
I'm no expert, but it might be worth a try. There was another post on 19th September "weak back legs" which also mentioned Glucosamine, which is really what encouraged us to go down that road.
Hope Barney is feeling better soon and finds his bounce again.
