Answers:
Mental is ( of the mind) according to most doctors it's the workings of the inner mind and how we relate to the arrangements around ud
It medium "of the mind." Mental condition is mind form. It's not physical, as the body is, but intangible.
if you suggest resembling when someone say "that dude is mental" it adage approaching the dude is "a bit off" or similar to "not right" or "overreacting"
typically "unstable" or act hot-headedly / irrationally