At 10 years of age we can start to see some cognitive dysfunction but it is not a common occurrence. I think he is picking up on all the changes in his life right now and we also need to get him examined by your regular veterinarian to make sure there is nothing medically that ha changed. At 10 years of age we can see liver and kidney dysfunction so blood work is also something I would recommend having done.
Now some holistic things we can do now
1. Getting him on some anti anxiety calming supplements to see if that will. Composure treats which have natural calming ingredients.
2. There is also a calming supplement called Zylkene that is a once a day that can help as well.
We can also work to make sure his joints are not hurting him ( low level arthritis pain can cause a change in personality) I would recommend starting him on joint supplements as well . A good one is movoflex
Once we have gotten him examined and made sure there is nothing underlying going on like metabolic disease for example then we can also look into getting him started on medication for anxiety specifically.
The supplements may be all he needs though so try those first.
For canine cognitive dysfunction there is a new diet on the marker that is quite wonderful and I have seen good results with called Bright Minds I think Purina makes it and we can get him started on that as well. Make sure when switching food always do it slowly over the course of a week to avoid any stomach upset.