Constant groaning is never a good sign, and old age may bring creaking joints and difficulty in getting from A to B. Just as old humans complain about little things in their retirement, in advanced dog years the dog may be psychologically disappointed that he can no longer run as fast or eat as much and has to rest for longer than before. Take him to a veterinarian if you are concerned it is caused by a deeper pain, and look for other symptoms. As for owners' depression, dogs are sensitive to those who own them so it may well be that he is reacting to the human's own facial expressions and thinks he has done something wrong. It is advisable, if concerned about your own depression, to seek some counselling for it and wait for a few weeks to see what steps your dog takes to adapt to your own condition. In any case, see a vet if the groaning does not improve over a prolonged period of time, and perhaps consider putting the pet down if it is getting too old, at the advice of the vet. Prolonging the dog's misery, looking into its eyes, may be unfair on the pet.
