Opioid withdrawal can feel like the worst flu of your life: aches, sweating, chills, stomach cramps, vomiting, diarrhea, anxiety, and trouble sleeping. Symptoms often start within hours of the last dose and can last a week or more.
Withdrawal itself is rarely life-threatening for otherwise healthy adults, but it is very hard to push through alone, and the risk does not end when the symptoms do. Once tolerance drops, using again can cause an overdose that would not have happened before.