“Dogs don't bark at nothing" is an adage that may or not be true. But they don't howl at nothing in their sleep. Recent studies by Dr. Matthew Wilson and Dr. Stanley Coren confirm that animals dream and quite often experience complex events while dreaming. If your dog Jimbo howls in his sleep with a fair degree of regularity and you wish to stop this, the best method of approach is to observe his behavior when he is awake.
Take your dog to the dog park as a first step. If you're wondering whether old Jimbo’s sleep-howls are a sign of distress, they could be -- howling in sleep or otherwise may be as simple as restlessness. On the other hand, they might not. Not to be cryptic, but a lot depends on your dog’s personality, what makes him tick. While your thoroughly modern canine doesn't howl as much as his wild, lupine cousin, his howl functions the same. As Dr. Coren notes: “Howling is actually a form of communication, which can indicate loneliness in an isolated dog, but often serves other social functions. Wolves howl to assemble the pack and also to reinforce the identity of the group.” Whether he's doing it in is sleep or in his waking hours, his howling can be disruptive, and it can be a sign of too much energy. Since it won't cost anything to try, go to the dog park or any place he can run off-leash. Jimbo might only need extra time at the dog park to alleviate his chronic sleep-howling.
Hire a behaviorist. It's equally plausible however that Jimbo doesn’t miss the canine connection and that this really is about you. Chronic sleep-howling could be separation anxiety manifesting itself in dream. According to WebMD, this kind of howling "is usually accompanied by at least one other symptom of separation anxiety, such as pacing, destruction, elimination, depression or other signs of distress.” Such cases can be handled through simple exercise or, in more extreme cases, via behavioral therapy by a certified behaviorist. A behaviorist will use systematic desensitization and counter-conditioning techniques to help Jimbo with his problem.
Take Jimbo to the veterinarian. His nocturnal howling behavior could be caused by serious illness. In such a case, yes, you would be right to be concerned. If he demonstrates symptoms of pain or illness, such as irritability, lethargy, vomiting, diarrhea or sensitivity to touch, especially in the abdominal area, take him to a vet immediately.