Dogs Behavior

Question
I am desperately seeking advice about my 13-year-old dog's very odd behavior.  For at least the past month, Otis has demonstrated severe agitation and discomfort.  He either refuses, or is unable, to sleep well; he walks the house, scraping his bedding or the carpet in a seeming "nesting" behavior; he does this especially at night.  He is also very clingy with me; not wanting me out of sight.  He has been examined by his vet and found to be fine; he eats well, goes for walks, and doesn't appear to be in any physical pain.  I am at my wits' end with this problem and I'm worried about him.  Can dogs develop mental illness, such as depression?   Could there be some underlying condition, such as Lyme's Disease?  Some additional information for what it's worth:  Otis was neutered three months ago and, in July, I added a new dog to the family.  Could these changes be a cause?

Thank you for your time.

Answer
He may have Canine Cognitive Dysfunction which is like Alzheimers in dogs.  Anipryl is the treatment of choice for this problem.  He may also have some form of separation anxiety and attention seeking behavior because of the new dog.  I would recommend a complete blood work up first to rule out any metabolic diseases such as underactive thyroid, diabetes or cushings.