What happens when you kill yourself in limbo?

Well if you kill yourself and the timer in the dream machine hasn't expired, you still end up back in limbo, unaware of the fact that you're still in there or the awareness that it's a dream becomes vague. If the timer on the machine reaches zero and you've forgotten where you really are, you accept it as reality (become older like Saito and die).

Hope that helps, I got confused too.

It's the only way out.

Originally Mal and Dominick stay in limbo for 50 years because Dom couldn't get Mal to believe that limbo wasn't reality until he planted the seed of the idea in her mind (Inception). He didn't do this until they lived through 50 years in limbo and he was utterly convinced, finally becoming desperate to get back to his children.

It is unclear what kind of sedation process Dom and Mal went through, but I believe that despite what happens to your physical body you must kill yourself in limbo or you stay there for what seems to your mind as eternity, slowly going insane. This is why they all wake up on the plane at the same time regardless of all the diversions the plan took, as they all physically wake at the same time no matter what, but their minds perceived different spans of time from hours or days to fifty years.

The tragedy of the movie is in saving his wife and himself from the madness of infinity, Dom plants the seed of an idea that consumes Mal in life, and out of love for him she tries to save him from the same fate by forcing him to kill himself.

Truly rife with irony.

Well, Mal and he liked it in Limbo. They were like Gods there and they could create an entire world. That was what they wanted. Then, Dom realized that they had to get back to what was real. To their children. So, he decided to commit suicide. At first, he didn't really think about it, because he was quite happy in Limbo. When he and Mal commited suicide, they ended up back where they were when they fell asleep. At least, this is believing the movie was not an entire dream and Dom is still in Limbo.

So, either you stay in Limbo, because you are confused about what is real and not (Look at Mal, she thought she was still in Limbo and the world wasn't real, but Saito thought Limbo was real) or you wake up again. Both is possible, I believe.

when you kill yourself in limbo you go back to the real world. remember how cobbs wife and himself had to do that to escape limbo the first time

You wake up in the real world if the sedative wore off.

Well, obviously if you kill yourself whilst in limbo you wake up, or at least wake to the level of dream before limbo. Or at least that seems to be what was implied in the movie, considering when Dom and Mal were in limbo for all those years, Dom performed inception on Mal, making her believe that in order to wake up they had to kill themselves, which is what they did, on the train tracks. So, when the train hit them, they woke up to where they were lying on their living room floor. And whenever Dom and Ariadne entered limbo to retrieve Fischer and Saito, Ariadne got Fischer - and herself - out of limbo and to the preceeding level of the dream by falling off the building, effectively killing themselves. I am assuming Dom did something to that effect with himself and Saito to get them out as well. So, my point is, the movie implies - but does not state directly - that the way to exit limbo is by committing suicide.

According to the movie, Cobb and Saito killed themselves to wake up. So apparently you wake up.

well if you're heavily sedated then i think you stay in limbo but otherwise you wake up, in the movie Cobb had to convince Mal to kill herself by planting that idea in her. that was in limbo and once they got run over by the train they woke up from limbo.