I can understand to a degree. I was depressed to the point of being almost non-functioning about 7 years ago. Since then I'm a lot better, my life is completely different but I still never expect to be 100% cured of depression. The important thing is to continue trying to improve your situation gradually and eventually you'll have a nice buffer zone of happiness to keep you further from the suicidally depressed levels it's possible to hit on the inevitable downer which is always lurking around the corner.

Some depressed people have a broken scale for happiness. If the normal range is 1 to 10, a lot of depressed people can only manage 1 to 7 or so, meaning they spend most of their time at a 3.5. The good news is that depression from a genetic/hereditary cause is surprisingly rare, about 95% of cases of clinical depression are environmental. Stemming either from the actual state of a sufferers life or their perception of it. With the correct actions to fix environmental stressors and the ability to view situations in an unbiased way it can be quite realistic to manage depression in the long term.

It's good that you're taking some time off though. Honestly, I don't know if it's possible for someone with your usual work schedule to live genuinely healthily, either physically or emotionally.