There are two types of losses or expenses that need to be covered to cover the risk of Critical Illness.
Hospital bills and allied expenditure: Your regular health insurance covers necessary hospitalization for all kinds of critical illness during your entire lifetime. To get the best coverage you must buy the policy before you suffer from any disease (which practically means right now, as no one can predict a disease). You must also ensure you have adequate cover relevant for a lifetime, especially when you hit your old age. Please ensure your health insurance policy coverage is calculated after factoring in inflation till you hit say 60 years of age.
Loss or curtailment of earnings: We have observed too many cases, where once a person suffers from a serious illness, s/he is forced to change her job to something less stressful, or even leave the job and rest at home for a good time. The way our lifestyles, the environment is - the chances of suffering from a critical illness are only increasing. It is therefore important to not only cover for hospital bills but also for the loss of income through a Critical Illness cover - either through a fixed benefit rider on a term life insurance policy or a standalone fixed benefit critical illness policies sold by all insurance companies. Here is something you can read: Comparison of Critical Illness Rider and Critical Illness Health Insurance Plan | How to choose (beshak.org)