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...

I am far from certain what you mean by "Existential Thoughts" but OCD thought loops are one of my meanest psycho ticks. The more I push them away, the more aggressively they fight back.
"Depersonalization" and "Derrealization" are terms which pop up quite allot in discussions of a psych symptom my shrinks call, "Dissociation." Dissociation is another of my meanest psycho ticks. It causes me to socially distance to radical extremes. I might as well be alone in a space capsule when I dissociate.
You've taken the important first step in writing it out.
One of the best gifts we give our thoughts is to release them to give our mind a break for calm.