I suffer from recurring depression with SI at the worst parts.

It's almost like you have the flu. It can actually manifest in a very physical way. You are extremely tired but restless. Can't sleep but can't get out of bed. Feel worthless and slow and useless and pathetic. You become irritable and engage in negative self talk and cannot break the cycle of negative thoughts about yourself even when you try to distract yourself with any number of activities. Pursuit of any kind of pleasurable activities seems impossible and only makes you feel worse that you can't even make yourself feel better with things that should work. Self destructive thoughts like this make you want to turn to drugs or alcohol or sex or anything that you think might get you out of the funk. When that doesn't work or if you can't even get the courage to do that, you get a constant barrage of intrusive thoughts and start making plans to end your life. Jump in front of a bus. Jump off a building. Jump off a bridge with bricks tied to your ankles. Get a tank of helium and a plastic bag and a big rubber band. You can try and try to think about something else but the ideas and thoughts become an escape from reality and in your sick mind they are the only escape from your suffering.

It's not pretty. Don't wish it on anyone.