Hemolytic reactions occur when the body's immune system mistakenly attacks and destroys its own red blood cells. This can happen during blood transfusions if the donor's blood type does not match the recipient's. The immune system recognizes the foreign blood cells as threats and activates antibodies to eliminate them, leading to symptoms like fever, chills, and dark urine. These reactions can also occur in conditions like autoimmune diseases or after infections. In severe cases, hemolytic reactions can cause serious complications, such as kidney failure or shock. Prompt medical attention is crucial to manage these reactions and prevent further health issues.