I don't think it's healthy to try to avoid down times, in fact I believe my best moments of clarity have come from the dark places iykwim? I was reading a great article (that I'm still trying to track down to post here) in which it has been found the we actually operate at a higher level when feeling down/depressed.

Maybe the emos are onto something ? lol

Although Miss Combat, I think you should also consider the highs you get from the physical side of your job. It's fairly known that lots of people get addicted to jogging because of the 'highs' experienced. Not saying you are addicted , but it may well be a physical thing for you too.