Well if it's any help, here's my two cents: to rewire your gratification circuits you need a lot of time and effort to alter your brains to accept some new ideas or behaviors. Took me a long time to get used to going to gym. Now it's like second nature. I know if you are really depressed it might be impossible to do it and other means, eg psychologist and medication, might be more helpful.
But the rewiring of your brain is the most important thing I feel in combating depression and getting somehow your lizard brain engaged in the "normal" things. For some reason I have felt that losing the connection to your primal desires (or the real you) is often the trigger, that will cause your body to tell you "hey, you are doing something wrong - please fix it". I know self-blame is the last thing any depressed person needs, but I think positive action and experiences are definitely key-part in overriding the negative thinking patterns. Things such as social connections, the feeling of belonging to a group and physical exercise.
Yet for certain, if you feel you are pushing yourself too much to me it says that there are deeper problems unsolved under the surface, that should be reworked with maybe a psychotherapist before going on a trip around the world. Or maybe it's a chronic chemical imbalance that just can't be fixed (eg Abraham Lincoln). Who knows.
To me physical exercise was like a magic cure that did feel like a natural depression medicine when you get the feeling of progress. Then other positive things started to build on top of it.