Heroin withdrawal. "withdrawal" per se refers to the symptoms which occur upon abrupt removal of a chemical to which one has become "dependent" upon. In the case of heroin, or other opiate compounds, the person may manifest severe, profound, symptoms that may include sweating, chills, shakes, hemodynamic changes and frank seizures that may become life threatening. Medical attention is necessary.
No. It won't kill you, but it won't be fun. It is a great thing to get off of, as it will open your life to new possibilities. Good luck.