Addicts commonly undergo withdrawal during rehab because their bodies became dependent on the abused substance. Recovering alcoholics may experience mild withdrawal symptoms like shaking, nausea and anxiety. Severe symptoms include hallucination, seizures and even heart attacks.
Withdrawal symptoms for recovering drug addicts vary depending on the drug abused, but are usually the opposite of the drug's effect. For example, cocaine causes hyperactivity and its withdrawal symptoms include excessive sleepiness.