A condition in which real or imagined fears are difficult to control is called Anxiety disorder.
What doesn't limit the range of moton from the things which you've mentioned would be age. Age per se doesn't really limit the range of motion - while there are factors which negatively influence our range of motion and which are strongly correlated with age, it is hard to say that age itself would be the cause of a limited range of motion.
I’m pretty sure it’s called relapsing
Where you start using again to stop feeling so bad
Yes, if not treated by a professional doctor.
