Critical illness covers: Critical illnesses are life-threatening diseases like cancer, heart attack, or kidney failure. The treatment for critical illnesses is usually very expensive. A critical illness cover leads to a lumpsum payment by the insurer to the policyholder on the diagnosis of a critical illness cover. It is important you opt for critical illness cover while renewing your health policy if you have not opted for it already. The addition of critical illness cover would, however, lead to an increase in premium cost.