I am not reading all the posts to this question, but simply posting from what I understand. I am a medium, I have had several readings where people who have done this who had a mental illness have came through.

What happens to them, they become energy again without the physical hang ups we have here on this side, so there is no mental illness any longer, nor do they have to suffer, or any crazy stuff you may here of. When they come through they will normally make me feel in one form or another how they were when they were here, in a way that I have the mental illness they had for a brief period, or communicate it to me in some way. They are fine when they pass, it is a physical thing here in the physical reality where they had to deal with, and experience their illness. Outside of the body we are pure energy, if they chose to stay that way they can, this is where you get lower entities that are closest to the physical world, so you can get ghosts, and stuff like that, but that is a choice. These people are more than happy to be away from what they were dealing with from my personal experience, they are happy to no longer have to deal with it. That's about the best I can describe from my personal experience, they don't cross over and stay mentally ill, nor are they forced into some negative place because they committed suicide, they are better off from those I have experienced readings with, and say they are happy and free of it there. I am not saying in any way that it is a good idea for those with a mental illness to commit suicide, growth through lessons still have to be learned, what I am saying is that they are ok, and not having to deal with the way they were when they were here.