Final answer:
Anaphylactic shock is the exaggerated immune response to a drug, leading to a massive release of histamine and resulting in severe allergic reactions, which can be life-threatening without epinephrine treatment.
Step-by-step explanation:
The exaggerated response by the body's immune system to a drug, which causes a massive release of histamine and other chemical mediators, is known as anaphylactic shock. This response is a type of immediate hypersensitivity, or Type I hypersensitivity, which is an allergic reaction. On initial exposure to a potential allergen, the immune system synthesizes antibodies. When exposed again, these antibodies cause mast cells to release chemicals like histamine and serotonin. In severe cases, symptoms such as airway constriction, blood pressure drop, and potential fatality can occur without treatment, namely the administration of epinephrine.