Millions of people have made insurance life choices and many of those people will likely have pre-existing medical conditions or immediate family members with health issues. Whilst this can be really concerning, the best thing to do in this situation is to thoroughly search the market for the best deal. There will almost certainly still be a policy available to you, but the greater the health issues usually means the policy premiums for life insurance are higher.
It's very important not to lie on your application, as any false information could invalidate your policy. Be careful not to omit or obscure any information as insurance companies can use third party sources to verify your application details. The insurance company may be able to get information about you by accessing your medical records and medication history, for example. As part of the process, you also might be required to have a medical exam, including fitness checks and blood and urine tests.