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.
Usually when we get a dog that is having problems with jumping, climbing stairs, etc, we suspect a disc or spine problem. If a dog twists suddenly like they do in play or if they slip, it can lead to a disc injury. An intervertebral disc that has slipped or ruptured up into the spinal canal causes inflammation of the spinal cord, which in severe cases can even cause paralyses of the rear legs. You can read about this here:
Large dog breeds sometimes suffer from a condition called degenerative myelopathy which can also cause problems with the rear legs. You can read about this here:
It might also be arthritis or hip dysplasia that has progressed to the point he doesn't want to jump or use steps. With arthritis though, they usually have problems rising but once they are up and moving around, they are more mobile.
Buffered aspirin can be given to a dog with a dosage of up to 5-10 mg per pound every 12 hours for pain. 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. Read side effects and precautions here.
Since you are going tomorrow, I'd probably hold off. Since he is eating and doesn't seem to have other symptoms, it doesn't sound like an emergency. Monitor him for other symptoms and if he does develop additional symptoms like vomiting and diarrhea then have him seen sooner.
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 .