this is a very good question.
i do believe the cry for help and just wanting to end it are deffinitely true, someone who jumps off a building isn't as interested in help as someone taking an overdose say, but saying this when in a major state of remorse or depression logically thought would go out of the window.
so this makes it very difficult, it has been documented many times of people attempting suicide and changing their mind half way, but this is mainly due to the subcociouses basic survival instinct.
very good question.......