I am Dr.Lisa; welcome to JustAnswer!
At 14 yrs, your dog is considered a 'senior citizen' of the dog world, and as such, he might start to show some aging changes.
It is possible that he had a stroke, however, with a stroke, we generally see signs such as dizziness, head tilt, overall weakness, rapid eye movements, etc. The diseases below are much more likely:
Any excess body weight will make any of those problems worse. A good place to start after an orthopedic exam would be with weight control (if overweight), and some X-Rays of his spine and hips.
The OTC product of glucosamine and chondroitin greatly help some dogs and are very safe to use. There are prescription pain medications (if he has a condition such as arthritis) such as Rimadyl and Metacam which can greatly improve his comfort and mobility.
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My dog, Gus, is not overweight (about 18 lbs for a miniature schnauzer). I find it strange that the change was sudden. About a week ago, he started dragging one back leg a bit and we thought he might have banged it or something. Then Sunday, he was the same in the morning but in the afternoon, he was having trouble standing. He walks kind of tilted to one side (which he didn't do before).
I realize he is old and I don't see the practicality of paying for a lot of diagnostic tests which would probably show that we can't do anything for him. He does not seem to be in pain, just a bit confused. His appetite is still good. Although we love him dearly, I don't see paying a lot of money to extend his life. We may take him in to see our Vet if he hasn't improved in the next while.
Thank-you for that additional information.
From that, it sounds much more like Gus has had a spinal cord infarct (which is actually a localized 'stroke'); it fits the picture very well.
Treatment is symptomatic, involving pain/anti-inflammatory medications, along with physical therapy - no expensive tests needed! If this is indeed the cause, the sooner that Gus is treated, the better chance he has of recovering.