Hypochondria is the excessive [too much] worry and fear of having a serious illness, despite having little or no medical evidence [proof or information from doctors or medical tests] to support [justify] such concerns.
For example, someone with hypochondria might constantly think they have cancer, even though all their medical tests show they are healthy. They may also frequently visit doctors for reassurance about their health, even when there is no clear reason to do so.
Very Simple Definition:
Hypochondria is when someone worries a lot about being sick, even if they are not.
For example, someone with hypochondria might always think they have a cold, even if they don’t have any symptoms. They might also go to the doctor many times, even if they are feeling fine.