Derealization and the kind of ocd symptoms or obsessive thoughts your are mentioning are not medical symptoms anymore. You only need psychotherapy. There are various aspects to psychological symptoms, ranging from medical to philosophical. Your ocd seems to be more related to your overall mental state of persistent unhappiness and existential anxiety. Your age of 41 years is ripe enough to deal with existential feelings. In early, young age of around 20, mind is not mature enough to deal with life's deeper issues. There are many thoughts and ideas to which we can get obsessed, and that too from very early in life. I have seen children from 8 years onwards who get occupied with thoughts of meaninglessness of life. So you also seem to be undergoing similar life patterns or thoughts. Try to see your symptoms placed within your overall life from a broader perspective , rather than merely medical. Allopathy is sufficient to work on ocd, but if that doesn't work, you must take regular psychotherapy. This is the only solution for you.