Understanding Fainting: Causes, Risks, and When to Seek Help

Question
Why when you stand straight, you can faint? Can kneeling on
your knees for long periods of time have the same effect? And
about for how long does it take for this effect to occur? Does it
cause brain damage, I heard that you faint as a defense
mechanism, does this kick in before brain damage may occur?

Answer
Why when you stand straight, you can faint? Yes, if you are not well.

Can kneeling on your knees for long periods of time have the same effect? not if you are well

And about for how long does it take for this effect to occur? it does not occur

Does it cause brain damage, I heard that you faint as a defense mechanism, does this kick in before brain damage may occur? Fainting is not related to protecting the brain.