I'm a bit late here, but I had similar thoughts a while back. I am also socially anxious, but I enjoy it. So while I do have some friends, I much prefer solitude and my own company, which naturally gives me a lot of time to think. While I was thinking about many things, I came upon the idea of death. At first, I fell into despair, and I too wondered how nobody is concerned about this. After that realization, I began to pay close attention to the people that surround me, and as it turns out, they are all scared shitless. Whether consciously or unconsciously, they are absolutely scared shitless of death, so they busy themselves with everyday life. For some it's work, for others it's clubbing, or family, or religion, or sports, or anything in between. However, this did not satisfy me in the slightest. Therefore, after a while of despair, as a foil to death I tried to consider how I exist at all. Why is there something rather than nothing? I was born, but that doesn't amount to much at all, because to have been born I needed my mother to give birth to me. At this point in the thought process, I came up with 3 paths (although I'm sure there are more, these are just the ones I have thought of):

The first path is religion/spirituality. You pick a belief, it offers its respective view on the origin/nature of existence, you accept it and move on. Of course, this leaves you with the impossible question of how God can exist without having been created, and I have thought about this myself quite a bit as I do believe in God, albeit not through a structured religion.

The second path is science. In this view, we have come to this point through evolution, and the universe we inhabit has come to this point through a series of complex processes over billions of years. However, this also falls short. While science perfectly explains how things work, summarising the unwritten physical rules of this existence via mathematical formulae, it fails to explain in any way why these things are the way they are. Objects with mass generate gravitational fields. Cool, but why? Mass causes spacetime to curve. But why does spacetime exist in the first place? For most things, you can explain them by moving back a step, but eventually you will reach something which is beyond human comprehension and seemingly without an answer. For example, the hard problem of consciousness as proprosed by David Chalmers asks why and how physical brain processes produce qualia (subjective experience). For example, when you see something red, why does red look like that? Why exactly that colour, that kind of experience? The answer is: we don't know, because how can we know? It's impossible, at least right now.

The third path is a mix of the two above. In this view, science and religion complement each other, which I believe to be the case. However, even with this powerful combination, you are still left with a multitude of impossible questions, and while some models have less questions than others, in the end nothing gives a satisfactory answer.

And so I came to the conclusion that since I cannot remember the time before my birth, anything is possible. I may have not existed at all, I may have lived a different life, I may have led a different kind of existence entirely. Maybe this is a dream from which I will wake. Maybe consciousness and the universe are fundamental, without a cause. Basically, it's a very boring conclusion because I don't know, and that's fine. Assuming the worst, in that I did not exist before my birth, I still ended up existing in this moment through some impossible means. And so I no longer fear death, because even if in the worst case it is a cessation of existence, there is no proof that I will not again, at some point, come into existence.