Anxiety Support Group
Anxiety is a physical condition marked by intense and persistent feelings of distress, fear, angst or dread. General anxiety caused by routine day-to-day stresses usually passes quickly and is experienced by almost everyone at one time or another. However, such feelings that linger over time and are very difficult to cope with, and which lack a clear cause, may indicate...

Perhaps medication would really help with your anxiety. It can do wonders for some people.
Talking to a therapist who is trained in anxiety can be very beneficial too.
You don't have to suffer with anxiety or depression. There is help out there. You are not alone. Best wishes.
You've taken the important first step in writing it out.
Keep writing. Sorting out all of the feelings, emotions, words, thoughts will help you find your better balance.
Human mortality is among the topics my own anxiety sometimes focuses on for my OCD psychoticks. One of many. A not-so-funny part of my own anxiety is that it seems to hopscotch through a genuinely irrational number of topics, often in a single day, but more often I obsess a single topic for unpredictable lengths of time.
In my own anxiety management, I take the focus off of the topic I am obsessing over and focus on the simpler fact that I am obsessing. One topic of obsession is as pointless as another. Ply therapy tools here. I don't **get** to make myself, my loved ones or any other human immortal. I do get to ease my anxiety and worry, should I choose to do so. It's a hard process, but it works if I work it and serenity is worth it.
But that is me and every case is unique. . .
Gentle support while you sort your own case. Welcome aboard. You are not alone. Listening. . .
One thing I try to remind myself is that my anxious or obsessive thoughts are not mandates. They are often just a lot of noise so I try to not give them anymore attention than they deserve. Sometimes just accepting them can take the energy out of them, for me.
If you are suffering from clinical depression I suspect these thoughts may be related to the depression. Not sure. But if you treat the depression it may help.