I broke my leg three weeks before going on holiday last year. My insurere sent me aform to complete giving details and costs involved The doctor also had to verify the medical reason for cancellation And as Ethel states one question was whether I had a prior condition that might have contributed. One of the things I forgot about at the time was the excess, which was �50 per person in my case.
You may be advisable to check with your insurer whether you are expected to cancel your flights ( if you can, I am not sure how many will allow you to do this & under what conditions ) because then you would only be able to reclaim the portion that you had to pay out.
Sorry if that last bit was a bit convoluted, it was just something I remember on the form.