I didn't want to scare or depress you on my post. Sorry. I just thought it might be better to accept the dog is OLDER than having a disease. I think with a "disease" or "condition" we can accept the issues we see in our dogs. However, when we know it is "old age" and just the "natural" course of a healthy life, it's harder to accept. A disease we can "cure", old age, we can't ignore!
My gut feel is the dog is going through the "change". It's no longer the young youthful puppy it was. It now needs a little more time and effort to do things. It's not time to panic. It may be a time to discuss "plans". Put some energy in deciding how to handle the final decision and when it may be appropriate. If it is cushings, would you consider putting the dog down or do you want to pursue treatments at it's age? These are things you and your family need to think about. How do you want the dog to live out the rest of his life?