I would like to hear more about depersonalization and derealization. First time I have heard either of those terms and I'm not sure what to think. I agree with Wild Coyote in that a mild dissociation from active thoughts is a form of "highway hypnosis" and may be why a person might go running in the first place(assuming they are in a safe place to let their thoughts wonder a bit). I'm not sure that is a concern needed to be discussed with a doctor but I am sure any doctor would welcome the topic.
As always, before I go running, I am well fed and not in an anxious or anemic state (the same rules apply to driving). Yoga keeps my mind more active than running, possibly because the muscles I am working on are less developed. Bird Dancer, please do share your thoughts on the other two topics