It's well known that when the brain becomes dependant on a psychoactive substance, withdrawals, rebound and tolerance are a given. Unfortunately, this is less known with prescription medicines, which are really the same thing but "controlled". After many years, the med can cause sometimes permanent changes in the brain; many develop depression after long-term stimulant use....thus the theory that chemicals are what cause chemical imbalance. It's not a popular theory, but it is a legitamate possibility given what is known about drug effects on the brain and body.
As far as rebound, what goes up must come down, and visa-versa, so the effects you have mentioned your son has from the meds is perfectly normal.