Almost all policies have a "preexisting illness exclusion." This sets a time following the policy purchase during which there's no coverage at all for any medical condition a person was treated for within some period just before buying the policy. Six months before and after buying the policy is the standard exclusion period. A shorter exclusion period usually means a higher premium.
Regardless of your medical history or current medical condition, if you have "guaranteed enrollment" in medigap, you can buy any policy sold in your state. Or you may have limited guaranteed enrollment in certain but not all policies, if you lost your existing coverage with a Medicare Part C Medicare Advantage managed care plan.
If you don't have any guaranteed enrollment, either because you waited too long to buy your first medigap policy or because you're now switching policies, an insurance company may refuse to sell you a policy or may charge you higher premiums because of your medical history. The company could ask to examine your medical records and even have you undergo a physical exam by an insurance company doctor.
