Sunstroke is a life threatening condition caused by overexposure to extreme heat. Also sometimes called heatstroke, this condition occurs when the body’s heat control system fails and it cannot lose the excessive heat. High temperatures can cause the body’s major organs to fail.unstroke is a life threatening condition caused by overexposure to extreme heat. Also sometimes called heatstroke, this condition occurs when the body’s heat control system fails and it cannot lose the excessive heat. High temperatures can cause the body’s major organs to fail.