When I was 21 years old, I got married to a woman who had never been away from her parents. When she was young, her parents had divorced but remained close but did not live together. After we were settled in Altus, Ok where I was stationed, she started asking me about certain parts of her body. She was really worried something was wrong with her. At first I checked her out real good but she kept on with it day after day. I didn't know what was wrong with her. I would tell her she was fine but nothing eased her worries. She eventually went to a psychologist to help her work through what was really bothering her. They prescribed her medicine to ease her worries. I had two years left of my four year term in the Air Force and this went on until I was out and we lived closer to her parents. I didn't realize any of this until years later.
It is miserable, not only for the person who thinks that they are about to get a disease and die, but for the people having to deal with the problem. You can tell nothing is wrong with them. You can tell them that but nothing convinces them. These people are labeled Hypochondriacs in the medical field.
Now, my family is dealing with this problem. My brother has started worrying about his health. He has been to the doctor and got all kinds of tests to prove nothing is wrong but he insists that something is wrong. Recently he had an anxiety attack and ended up in the emergency room thinking he was having a heart attack. I have told him he needs to get counseling but so far it is going in one ear and out the other. They did some tests on him to determine what was wrong with him but didn't find anything after a stress test and sonogram. Still, he thinks they are missing something. If he doesn't seek help, he will most likely end up in the emergency room again.
As someone on the outside, there is nothing you can do to convince Hypochondriacs there is nothing wrong with them. It is on them to figure out they need to see a counselor. That is something my brother has not yet figured out for himself even though we keep telling him. It's almost like an alcoholic or drug addict who has to come to the realization that they need help.
If they get to where they are hurting themselves (scaring themselves to death), it is time to get psychiatric help by forcing them into it. It's not something anyone wants to do but sometimes it is necessary. I'm hoping my brother will realize he needs help and takes the first step.