I never wrote a suicide note, but during my darkest days, I kept a journal. I still have both books, though only one was filled completely. It contains just about what you’d expect from someone who was descending into psychosis - rambling, nonsense, theories, paranoid ideas, and, of course, instructions on what to do should I disappear or turn up dead, obviously at the hands of the government that was surveilling me and had plans to stop me from completing my mission (bringing the government down by becoming an inside man).
Note: I believe this was before I joined this forum and before I had my “epiphany” that I had to die to complete my mission.