You don't know it at the time. You truly don't. Unless you've been there it's difficult, nigh on impossible to understand. It can't accurately be explained or demonstrated. I've been there. More than once. I expect I'll be back there too. For now I'm okay, but I have to take each day on its own merits and try not to let extreme emotion take over - positive or negative. The worst thing is knowing there is no cure. Medication helps sometimes, as does CBT or counselling but they're the equivalent of the boy sticking his finger in the dam wall to hold back the flood. TBH I can imagine many people feel that death/suicide IS the cure.