If your dog is suddenly afraid of getting on and off furniture, he likely has a good reason. In many cases, when a behavior stops, it's because an unpleasant consequence has deterred it. Fortunately, with your gentle guidance, negative consequences can be transformed into positive ones, so your dog can be helped to enjoy climbing on furniture again.
A Painful Experience
In some cases, reluctance to climb on furniture can be caused by pain. For small dogs and puppies, jumping off furniture is a leap that can cause injury. If you own an older dog who no longer wants to jump on or off sofas or chairs, it could suggest the onset of arthritis, intervertebral disk disease, pain or injury to the rear legs and muscle weakness as seen in Addison's Disease. Even though your dog may seem fine, consult your vet as sometimes injuries aren't readily recognizable. X-rays and other diagnostic testing may reveal the source of problems.
A Scary Experience
Other than pain, a scary experience may have a negative impact as well. Your dog may have jumped off the furniture and found a slick, wet floor causing him to panic from the unsteady sensation of his feet. He may have fallen or landed harshly. If your dog was scolded for jumping on the couch or was startled by a noise as he was getting on or off furniture, it may have scared him. Dogs learn by associations, whether positive of negative.
Addressing the Fear
To help your dog gain confidence again, you'll need to address the underlying problem. If your dog has a physical problem, his reluctance to jump may resolve once treated. For chronic conditions, you may need to install a dog ramp or steps to prevent pain and risk of further injury. For slippery floors, you can use rubber-backed rugs. If your dog got startled or traumatized for some reason, you'll need to work on making getting on and off furniture a pleasant activity again. Since dogs learn through associations, you'll have to reprogram your dog's mind to create positive associations that will replace the bad ones. This is accomplished through counterconditioning.
Helping Your Dog
Once your vet has ruled out a medical problem, you can teach your dog to enjoy being on furniture again. Forcing your dog to climb up or down all at once may worsen his fear. Instead, find a pace your dog's comfortable with and reward every little step spread over the course of several days. Start by giving a treat to your dog when he's near the furniture, looks at the furniture or sniffs the furniture. Use a treat to encourage your dog to stand against the furniture and reward him for it. Finally, encourage him to jump up. When he does, praise and reward him with a jackpot of treats, feeding him several bite-sized treats in row. Make sure your dog gets plenty of rewards as well for jumping off.