Though I know the feeling of 'glass is half empty', I feel I don't know the feelings you have {lot of feelings here lolololol}. That said, I have my days in which I doubt everything, in which I think the world is against me in all aspects, in which I get no single thought turned into something positive, in which I am not able to put even a small smile on my face. However, I also have days in which I feel the total opposite like a 'glass is half full' type of mindset. I believe I have more (many more) of these 'full' days than 'empty' days. At least, it's my drive to try everything for that. I even test things like adjusting my sleep rhythms, eating patterns (and content) and even my approach to work to increase the number of positive days, or better said positive moments. Over a decade or more (likely three plus decades) I learned to switch between the 'empty' feeling to the 'full' feeling in a matter of minutes; Not always (well, maybe less than most of the time) am successful when trying, but for sure at times it works.
You wrote about acceptance of those that are dark, those that are in the space of 'glass is half empty'. My worldview is that we all must make at least an effort to accept all kinds of people, regardless of what their beliefs are, regardless of how they view life. Something most of us not even trying to do these days. Many of us live in our own tunnels and when someone or something doesn't fit into that tunnel, we don't want to accept it. But now I'm digressing from the topic of your post. I do hope you'll be able to find ways for living that don't require strong words such as 'constant pain' and 'unbearable' to describe it. Channelling the pain into doing something for others, is to be tried for sure! Am sure you make others happy and hopefully that can bring some happiness into your own life.
I adjusted my sleep routine/time/rhythm and hopefully this will work for me too. So far okay, I will wake up early finish all my work tasks then sleep again. I feel more normal sleeping late than staying awake all night long. As I get older, getting 8 hours of sleep becomes a challenge. When I slept well, I do feel positive like I can conquer everything lol. Sleep is so basic. We need it to feel good.
I agree however difficult this maybe. I feel like we all live based on our preferences.
Sleep can have a large influence on our state of mind indeed. Covid turned me into going to bed earlier, resulting in more hours of sleep. Covid gave me also a more regular wake.sleep patterns, since no night parties around to attend to and causing me to sleep in the daytime, or just skip a full night. Though now everything is open again, I see myself getting back into that nighttime stuff again. Though not too frequent, hence good to handle so far 😉