If reincarnation is true, then why live a life you don't like? If someone's life is completely miserable, wouldn't dying on purpose pretty much work like a reset button?
To be honest and I'm somewhat embarrassed to say this, if I believed in reincarnation and had no doubts, I would turn to mindless self indulgence. Why would I worry about health if I'm destined to live another life?
If you are living a life that you do not like, it is incumbent on you to try to make your life better. The only thing pain and sadness should teach you is not to go through pain and sadness. Well, don't get hung up on them at least. Ask yourself what you are contributing to your life that is furthering that sense of misery. Are you doing anything to change your condition, as it were? Have you tried to change your life circumstances?
Suicide is not always a bad thing,
but it should be a very last option after all other avenues have been exhausted. There are always choices that can be made. At the very least you may find happiness incrementally... one bit at a time.... At times, you may feel you are getting nowhere, but it's at those times that you should sit back and ponder what you could be doing more effectively. Is an attitude change in order? Is it time to move or get a new job? Is it time to cash in your girl friend or significant other? Etc...
But.... the real beauty of reincarnation is that you do not have to believe in it. It DOES NOT MATTER if you believe in it or not. Your belief does not affect any reality save your own. The thing is don't get too hung up on the models of reincarnation that are available on the bookshelf. They are quite simply put, incorrect. Karma simply is not a part of the equation and though actions do have consequences, it is impossible to trace what action precipitated what result. The only guideline is your sense of well-being and a sustained sense of happiness. The route to unbreakable happiness is through value fulfillment. Value fulfillment is the art of expending energy in a particular area and seeing the fruits of your efforts. Moderate your expectations and you should be OK.
The thing is reincarnation is a much larger, much looser system of activity than is normally imagined. It is a system that has very few rules and is meant to demonstrate to the individual how their thoughts and beliefs literally mold the world they experience. If your life is crap, check your beliefs, thoughts and expectations.