FEAR
If "you" are one with the Flow, there is no problem. How can there be fear when there is only one unitary movement of reality?
But when "you" (which is thought doing that imaginary split) separate "yourself" from the movement so there is the illusion of "you" and the Universe as separate (the Horizontal Conflict - subject vs object), which is only and imaginary perception, then problems emerge (again, as thought).
"You", the subject, the "me" is produced by thought to act on the Flow of reality, so you are (in the imagination of thought) separate from the Flow..
So that is the mechanism. By inventing an imaginary "experiencer", thought produces imaginary fear as well. But then fear, being thought, a bio-chemical movement in the brain, is able to reach the level of the body/matter as well (the Autonomic aspect of the META Process of thought). So fear/stress/anxiety is dangerous, it can cause a heart attack. It's important to understand it all and realize how important freedom from the process is.
Freedom from thought is absolutely necessary and only UP is the correct perception, without the illusory division/separation into the subject - object, produced by thought. Only in the new pure perception of reality fear dissolves. In fact there is only the unitary undivided flow, movement of reality, the Universe.
If you are the Flow of that what is itself there cannot be fear (which is imagination, knowledge, control and the "controller", desires, pleasures, goals, etc, the whole content of consciousness), for there is only one movement.
If understood correctly UP is not a positive movement (for all positive movements have goals, purpose in the horizontal conflict), i.e. "I do it". In UP there is no self/experiencer/I. The I is only a false product of thought (sometimes functional). That means UP happens when the false illusory movement of goals, time, control, is understood and ends.
In reality there is only one unitary movement. What sees is all there is. If we ignore certain nuances, we could say that that one movement IS UP.
UP = the Universe. The Universal energy does UP in the brain. Only when we are awake (the Second Awakening, so the brain is not cluttered with thought with its control, goals and the self, we are It, the one movement of Reality where fear cannot enter.
