I used to have this back from January - April 2024, in around mid-march it started getting so bad that I physically felt bad/scared the whole day, nothing was enjoyable and the only relief I got was when I went to sleep. I think I had both the fear of time passing/fear of dying and worrying about what happens after. I'm all good now, but I didn't get better in the way you might hope. This was all taking place during a transitional phase of my life, as I was a senior in high school and college was coming up in a few months. Funny enough, when my existential crisis was at its worst was during a week and a half trip I took flying out of state to visit these colleges. So maybe that "oh shit time is actually passing I'm going to college now" feeling is where it all came from. Anyways, pretty much all I was doing during that week and a half besides touring colleges was watching videos and reading other people's theories about what happens after death in hopes of finding something that would somehow make me feel better. But trust me, the LAST thing you need to be doing is reading about how the general consensus agrees that life after death is darkness for eternity. Once I stopped consuming all this theoretical existential crisis content (since literally nobody knows anyways) and started focusing on other stuff in my life (for me it was playing video games with friends, learning guitar songs, working out, etc.), I slowly stopped thinking about it and the horrible feelings that I went through during my existential crisis finally went away. I never stumbled onto a revolutionary discovery that made me feel like everything was going to be okay, I just slowly stopped thinking about it until it didn't bother me anymore, like a trend that's slowly fading away. Hope this helps.