Firstly I will say, not sure if Vitamin D really helps as it was mentioned here. When I had my blood test done, the GP told me she is shocked that I am still standing and awake at the very low level of Vitamin D that I have.
As for suicide, honestly no I haven't, therefore I cannot pretend to know how you feel, and hopefully professionals out there who deal with this are able to help you.
I will open up a little about myself, not sure how helpful this will be. Maybe someone else can relate who has not felt that way and can perhaps share a little that hopefully can turn into something useful.
I have at times thought about why people that are close to me that I know have told me they felt suicidal or attempted it. By close I mean we have gone to primary school together and years later are still friends as adults. The only difference between their life and mine from what I can tell is I am extremely busy (i.e. always working, two jobs at times and going out of my way to help others when they ask even though deep down I know this just adds to my work load already) and for most part of my life I have been alone (till I got married). So not sure if my mind is so preoccupied that I do not have time to think about it, or because from a very young age I was always alone, or perhaps a combination of the two. Maybe my brain got wired different due to my childhood and I have learned to cope with it and don't have that emotion of feeling sad when alone,( i.e. my parents would go to work when I was 3 and the neighbour would check in on me few times a day) so I would keep myself busy. I have never really felt the need to have many people around me and at times it is very draining dealing with people.
There was a time in my life with a back injury that lasted for 2 years. This COVID lockdown doesn't feel that bad for me because of it. However, even then, I was working from home. I wouldn't walk much or move much, but would sit at my computer desk working.
Even as I type this, it is 3:20am, even when I sleep, my mind is always switched on and thinking. I once did a test for a week to see how much REM (or is it REN??) sleep I get, and on average it was about 6mins a day.
The final thing I can add, is I am very good at bottling up my emotions. Whether it's good or bad I do not know as at time I do explode and mainly feel anger. Qt least I don't feel the opposite where i wish I was dead. Then when I calm down, I bottle it all up again.
So what advice can I give from an untrained perspective? Not much other then my own life experience, which I think the main factor for me is keeping busy and because I help others. I get joy out of seeing others succeed. It is almost like a drug seeing that my time was able to make a difference to someone.
As I mentioned earlier, I cannot judge nor pretend to know how you feel exactly. But one thing I know is no matter how bad you think you have it, I am sure there is someone worst out there. Also as a person you have control on what you do in your day. I think you need to find the right activity for you that makes your mind reward you for doing something. You may have to stat with something small but do something that has an end goal and if you get there feel good about getting there.