India – Health Insurance – Does the base premium is fixed for all the years or increases even if not claimed?

In India Health insurance companies coveres pre-existing diseases after 2, 3, 4 years of paying the premiums regularly. 1) I am having bp and sugar. Does my diseases will be covered after 4 years ?? do i have to disclose after 4 years, or at the time when i got a need to admit as in patient. 2) Second doubt, does the base premium is fixed or does it increases based on age slots. Even we not applied for claim kindly advice. thank you