The brain’s anticipation of threats is an invaluable survival tool

the correct word should have been " WAS" (an invaluable survival tool.

Erm. Psychopathological anxiety from mild to severe is one thing. The greater anxiety is existential, though unfortunately such a word which was difficult enough when it started has now been smoothed to meaningless, except perhaps here as a quick and dirty pointer to such issues as: dread of condemnation by others, guilt, meaninglessness, fear of annihilation of self (a la Kafka) and most obviously fear of death.

Keep in mind, that fear of death can be reasonable and palpable, and an anxiety may be subconscious alarming reaction for real somatic or social deviations.

good news. i've got some memories that should be blunt immediately! ..