David has a diagnosis of schizophrenia and buys a standard travel insurance policy through his travel agent. The policy says it covers medical treatment, including for mental health problems. However, there is a clause in the small print that states this does not cover pre-existing medical conditions.
While he is travelling, David becomes unwell with problems related to his diagnosis and needs hospital treatment. In this case, this treatment would not be covered by his policy, and David would have to pay for it all himself.