EDIT: This guy refers to a "detox phase" where the "chemicals come out" but he is mistaken; what he in fact is referring to is the body's cycling of all of it's behaviours that start to build back the natural endorphin deficit that was offset when exogenous opiates were added (homeostasis).
In fact, there are many phases - I still was getting withdrawal symptoms for over 2 years when using Meth (40 year old user of opiates and opioids now aged in his late 50's).
But anyway, here he is:
YOUTUBE:I go over some of the phases and symptoms associated with opiate withdrawals and also Introduce GABA and 5-HTP supplementation.