My name is ***** ***** I’ve been involved professionally with dogs in the health and behavioral fields for over 18 years. It will be my pleasure to work with you today.
Initially I can think of a couple of reasons why a dog might not be able to climb stairs or jump including an anal gland issue or a disc injury. I know you are thinking that there was nothing to cause a disc injury but often a disc issue is degenerative in nature.
An intervertebral disc that has slipped or ruptured up into the spinal canal causes inflammation of the spinal cord, which in severe cases causes paralyses of the rear legs. You can read about this here:
A disc injury can be very painful and dogs become very scared as they don't know just when the pain might hit as it might only happen when the dog moves a certain way.
Buffered aspirin can be given to a dog with a dosage of up to 5-10 mg per pound every 12 hours. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet. The aspirin may need to clear your dog’s system before other medications can be given, so keep that in mind if you decide to give aspirin and be sure and tell your vet when your dog is seen. Personally, I'd hold off on Aspirin if you can get her seen in the next day or so. Read side effects and precautions here.
An anal gland issue might also cause a dog to not want to jump or climb stairs as those actions will pull the skin in the area around the rectum where the glands are located. If the glands are very full or infected, this will caue intense pain, and the yelping and trembling you are seeing. If your dog has been dragging their behind on the ground or carpet and their anus area has a bad odor and swollen, it can be symptoms of an anal gland problem. You will want to check to see if your dog's anus is swollen. This may cause a dog to continue to lick the area.
The anal glands are 2 sacs on either side of the anus at about the 4' o'clock and 8 o'clock positions. If your dog is continually licking their anus and dragging it, it could also indicate that they are full. This problem can usually be resolved by emptying out the glands. To empty them or express them, you will want to cover the area with a tissue and press your finger on the dog's anal glands with an upward motion. A foul smelling liquid should come out. If nothing comes out and your dog appears to be in pain, you should take him to the Vet. Your vet can do this easily, as he is experienced at it.
Excellent site on anal glands
Unfortunately, you have to determine which is the cause of her pain and have her seen. Both questions will likely need the services of a Vet and pain relievers and/or anti-inflammatory medications will likely be needed to help relieve her discomfort. I would try to get her in today so she isn't in pain for the long weekend. .
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.