Catastrophic health insurance covers you for the big expenses such as major medical and hospital expenses, but doesn’t pay for the smaller costs such as doctor visits, prescriptions, etc. For example, if you got in a car accident and had to spend time in the hospital, you would be covered. However, if you want to visit your local doctor and get an allergy prescription you would not be covered.
You have to consider what things you want to be covered, your deductible (how much you pay before the insurance kicks in), and the maximum lifetime limit of your benefit. You can start by visiting a local insurance agent or try this health insurance quote page.