Travel insurance policies will usually define what the insurers consider to be a pre-existing medical condition, however this does not mean that they will cover it. Whether the policy includes cover for your conditions or not you will still need to check the important health requirements specific to that policy.
For example an insurance policy might operate on the following basis:
1. To be covered you must be healthy and fit to undertake your planned trip;
2. The insurance will NOT cover you when you are travelling against the advice of a Medical
Practitioner (or would be travelling against the advice of a Medical Practitioner had you sought his/her advice);
3. The insurance will NOT cover you when you are travelling with the intention of obtaining medical treatment or consultation abroad;
4. The insurance will NOT cover you if you have any undiagnosed symptoms that require attention or investigation in the future (that is, symptoms for which you are awaiting investigations/consultations, or awaiting results of investigations, where the underlying cause has not been established) or have been told about a condition that will cause your death.
Please note that this is just an example, you will need to check your own policy for the relevant health requirements.