Please don't take this as a cry for help or as a whine or a sign of crippling depression, or worse, hardcore memery, but on every passing day, I get more and more convinced that I'm going to kill myself. Hopefully not soon, probably in my 50s or 60s in a very subtle, dignified, and filled with plausible deniability-way, but who knows where life might take us 5 minutes from now. My genes are fucked, most of my ancestors are either mentally or neurologically ill, and I don't want to make an ass of myself and I want to control the way I leave. I just hope that I'm still living at a time and age where such a subject is still taboo, and not the duty of every untermensch or elderly citizen.
Ok so I'm going to give you some tips, just beware it's not the cheapest way but it's the best one in the long run:
Professional help: go to the best psychiatrist in your town, talk about what's happening and get on some SSRI (no benzos). You will feel useless and physically tired for a couple of weeks until they kick in. These alone will not solve the problem, but they'll keep your mood stable; let's say if before you're feeling on a wild rollercoaster now you're cruising. It's not an enjoyable cruise, it's like cruising through Iowa or some other shitty midwest state, but at least your thoughts will become more rational and you can build from that.
Pair the shrink with a good psychologist and have a meeting every week/couple weeks. Again, you will feel useless, but it works.
I say good because there's always the cheaper one but then he'll give you the wrong meds/advice and you end up spending twice the money and time.
From that, after what it could be weeks or months, you focus on what makes you feel worth: for me it's skating and solving civil eng problems.
People will tell you to take a break, do yoga, meditation, drink yourself to sleep, don't overthink and that's cool if you've been dumped by your girlfriend or lost your job, but if you're born with a big serotonin deficit all the fresh air in the world won't make any fucking difference.
Last but not least: keep your friends out of this. Good luck.