The catastrophic health plan is a high deductible health plan (HDHP) and a way of having immediate coverage for the “big stuff” -- like a sudden visit to the intensive care unit.
Generally, the catastrophic health plan allows you to have immediate coverage for hospitalization, surgery, ER or trauma care, ICU, and medical tests performed in the hospital without needing to cough up a lot of dough on a regular basis for monthly premiums. However, these plans only cover immediate (and sometimes very limited) care. Nothing else. You cover the full bill out-of-pocket for all other care (like a normal visit to your doc).