I'm of the opinion that HA isn't a disorder on its own, but a symptom of one, such as OCD or GAD. The reason I feel its important to make this distinction is because it's more of the underlying thought process that is important to examine instead of the symptom. For example, if your problem is OCD, you might be deathly afraid of leaving the stove on and burning your house down. You develop a compulsive checking habit and it fuels your obsession that you might burn the house down. As your anxiety grows and grows by feeding it through your checking behaviors, you begin to doubt more and more if you've indeed left the stove on, because that's how the anxious mind works. After a certain point, reassurance and checking does not alleviate anxiety anymore but the brain believes that it is better than nothing and thus is helping.
But extend that situation to health anxiety. You are deathly afraid of getting a heart attack and as a result you are constantly checking aspects of your heart health to make sure that you're okay. You'll check things on google to get reassurance that you won't die of a heart attack. You'll check with doctors. You'll check with other people. You'll check the statistics. "Only .02% of people under 30 die of heart attacks (made up statistics)? Well I bet those .02% never thought they'd die from a heart attack at my age either!" Your mind focuses on the chance it might be you, and not the 99.98% chance it isn't you. Your constant checking and seeking of reassurance only serves to deepen the anxiety and obsession.
Both two different situations, superficially, but the underlying unhealthy thought process is the same. You have some sort of uncertainty/doubt/anxiety/fear, you respond to that fear with checking/reassurance/coping of some kind to try and make anxiety go away, your brain thinks these things are helping you so it allows your obsessive thoughts about the subject to grow and grow and grow. All the while, this cycle is making you more and more anxious and the reassurance behaviors become more and more futile.
It is absolutely tough and time consuming to be in that state of mind.
I have been diagnosed with OCD, so I can say for sure that my HA is related to OCD...but I don't know if that applies to everyone who has HA. All I know is that the way people with HA behave is extremely similar to OCD in almost all case I've read, so I believe the same general advice is beneficial to anyone with HA.
What has helped me immensely with all forms of anxiety, including HA is this.
1. Learn to accept uncertainty and learn to live with imperfection
-It seems that many people with HA can have perfectionist tendencies and so they want to know that they are perfectly healthy and free of health problems before they feel they can move on and live a happy life. Additionally, there is a huge desire to want to KNOW for SURE that you are okay before you feel you can move on and do other things. This is part of the disorder. The reality in life is that there is never any certainty ANYWHERE. There are different degrees of certainty, but what an anxious mind usually wants is complete reassurance that nothing bad is happening. What makes this a disorder is the "complete reassurance" part. Part of the disorder is the mind's amazing ability to doubt everything. If your mind can pick at a tiny detail that doesn't fully seem to explain something, your mind will amplify that and begin to doubt that you are okay even in the slightest bit. Your mind will ALWAYS find something to question or doubt.
You must learn to embrace when you simply do not know what is going on and you do not know what will happen. This is very scary to admit at first. You will feel a loss of control and an increase in anxiety for maybe minutes, hours, or even days. If you want to break out of the anxiety loop, you have to become friends with uncertainty. You have to learn to embrace the anxiety, which takes time to get good at. To eventually experience less anxiety in general, first you have to experience more of it.
2. Completely stop checking/reassuring/coping behaviors
This is equally as important as the first step. In response to anxiety, you might google symptoms, call your doctor immediately, contact them frequently about different questions or maybe repeat the same questions, talk to your family members about the same subject frequently, seek reassurance from people around you that you are okay, monitor your body very closely, check things in the mirror, checking your pulse to see if it is normal, googling normal numbers, googling heart attack cases to see if they match up with you, etc.
These behaviors might be reassuring AT FIRST. Left long enough, however, they will begin to consume you and allow your anxiety to grow about a problem that you should already have moved on from to continue for a long period of time. Eventually, your mind will find problems and faults with ny form of reassurance. "How does that person know i'll be okay? Did my doctor check enough? What if he was being careless? What about that guy on the internet who died from a heart attack at 19?! Okay, three sites told me i'm probably fine, i'll try and find another site just to be completely safe."
This is where ERP therapy (exposure and response prevention) comes in really handy. You gradually expose yourself to your fears and anxieties, and you make every effort not to give into those anxieties with a coping/checking/reassurance behavior. It's extremely tempting, but if you can remain resilient, you have taken major steps into living a more anxiety-free life.
3. Start with small anxieties and work your way up.
If you have tons of anxieties or are anxious about other things, it might be helpful to cut out one compulsive behavior at a time. Maybe it is too much to stop asking for reassurance for everything. Perhaps you are only slightly afraid of one thing but absolutely terrified of another thing. Start by not checking on the smaller problem that you would feel more able to handle.
The point of this step is that if you have massive anxiety, generally doing the things you need to do which will ultimately bring you to peace of mind will require big jumps in anxiety. If you have too much, this can be too frightening and you might be too scared to move forward, or cause harm to yourself in one way or another (googling binge for example...now you know too much and will never be able to rest!)
4. When it comes to therapy, you have to kiss a lot of frogs before you find your prince/princess.
Hardly anyone likes the first therapist they go to see, especially if they are uncomfortable with the idea of therapy in general. Therapy is a perfectly useful tool that all types of people benefit from. Many seemingly normal people on the outside go to therapists, and many people who don't really have diagnosable mental health issues also see therapists. Everyone has mental health, even if one doesn't have a specific disorder, and anyone can use it to help take care of their mental health.
Likely, you will have to try a few therapists before you find someone you like and trust. The therapists know this too. When they are in there doing your intake, that is just as much of an opportunity to ask questions of them. You are both feeling each other out to see if it is a good fit. They get that. It's not offensive if you thank them for their time but you don't feel its a good fit. Mention from the beginning that you are still in the process of finding the right therapist and you will find they totally understand.
Don't let one off therapy session ruin all of therapy for you, it can be really helpful to work with someone you trust on these issues. They can help troubleshoot any problems along your path to recovery, as well.
I hope this was helpful. It really sucks to be so focused on health for no reason. I promise you it will be so worth it when you can realize for once in your life that you are indeed healthy and enjoy life instead of worrying about what may happen around the corner (that usually never does happen).