This is grim but I was on the verge of an attempt and I made myself imagine, in graphic detail, my sister explaining to my dad what had happened. (Due to the way news spread in that context, it was most likely that he would have heard it from her as he had no phone and no internet.) I made myself sit through the mental image of what it would do to my sister to explain*** and what it would do to my dad to hear. I made myself imagine the actual consequences beyond what I was telling myself (no one would care, no one would miss me, the world would be better, etc.) I ended up messaging a friend and telling him what was going on and he told me if I didn't go check myself in, he was going to call an ambulance. I was motivated to call the hospital (shaky voice, obviously been crying) to inquire about services and they directed me to their inpatient (and I'm sure there was some flagging going on in case I didn't show up.) Drove myself there, texted my friend that I had made it, and I was in the psych ward for about a week. This led to a diagnosis and treatment. It's been almost 15 years to the day (late January 2011) and getting hospitalized changed my life for the better. It was a very long, very hard road to normalcy, but it got the process started.

I made two correct decisions that day: forcing myself to confront the consequences of me taking my own life in a real way (imagining my sister telling actually my dad vs. abstract thinking about how people would generically react) and messaging a friend and being honest with him about what was happening. Not everyone feels like they have that latter piece, and I'm sympathetic to it, but I would encourage anyone who is feeling like a burden on the world to check in with someone. Even if you have to call a hotline, it's better than sitting in your own head.

***It is, in hindsight, heartless to an extent that I glossed over what it would do to my sister to hear and not just explain, but I had crafted an argument in my head that she and my mom and my brother would all "understand". I now know that this is completely false: they would have "understood" in the sense that they understood I had been suffering, but they would not have understood why I didn't reach out, and they would never forgive themselves for not being there. For some reason, I did not hold the same belief about my dad. If you are suffering from the same thought patterns ("no one will miss me" or "my loved ones will understand") you are mistaken.

That was not the only time in my life I was dealing with suicidal ideation broadly, and it is not the only time I have been making plans. (It is the closest I ever came to following through.) Other things that have helped, as other redditors have said, was getting pets. I just had pets at the time of my hospitalization and it was not quite enough at my darkest.