We see these phenomena consistently in people. We also see them consistently in animals being held in captivity not suited to their species' specific needs. I am less and less convinced that this block of anxiety, depression and procrastination is a disease but a reaction to an environment in the broadest sense inherently unsuitable to humans.

I've heard the idea from Somatic Experiencing-- unfortunately, I haven't found anything that goes into detail about that particular angle, except that part of it seems to be about having a tribe-- it's not just about spending time out of doors.

I'll be keeping an eye out for information on the subject, but meanwhile, you might want to look into Somatic Experiencing and Peter A. Levine.