A pre-existing illness means any health issue that the proposer has been facing prior to
purchasing an insurance policy. This condition includes all the health issues ranging from High Blood Pressure, Thyroid, the usual suspects like diabetes, asthma, etc. Not disclosing or hiding any information from your company, firstly you breach the principle and secondly would put your claim in danger. Even though you won’t be covered for the pre-existing conditions in the starting few years of your policy, you would ultimately enjoy the coverage when the waiting period gets over.
So to ensure that your health insurance gives you adequate cover do not hide any ailment and clearly declare them before buying the policy. This will ensure that you have a clean settlement process for all your future claims.