One morning a few weeks ago, my 5.5 year old Maddie would not come down the stairs. She'd been jumping around the day before chasing bubbles in the yard, so the vet suggested she was stiff. I got a neighbor to help me bring her downstairs using a towel around her belly as a harness. I kept her away from the stairs for a couple of days, and things returned to normal. Then, yesterday afternoon, she started showing the same reluctance to go downstairs. She has no other symptoms of arthritis or hip dysplasia. She still jumps on the couch, bed, and into the car, runs around excitedly and is has not slowed down on walks. When comtemplating the stairs, she puts her two front feet on the first stair but then is desperately afraid to go any further. Her back legs shake at the prospect and her heart beats wildly. I can't tell if she is afraid or in pain. Our stairs are hard wood, and we've taken steps to have a runner installed, but that's still weeks away. Any thoughts or suggestions as to what may be going on?