Dopamine is a chemical messenger in the brain that is responsible for: mood, movement, higher thought processes and the sense of well being.
A lot of the side effects with gambling addiction withdrawal are due to these low levels of dopamine and other neurotransmitters that are released when the addiction stops.
The worse the addiction, the more intense the withdrawal symptoms. Gambling addiction withdrawal is also due to membranes in the brain being destabilized.
This means that the ongoing addiction has altered the electrical and chemical balance of the brain and that it does not function normally. This brain destabilization may take months to year to correct.