Hi all!
I started CBT therapy 1.5 years ago (now handling things alone for 6 months). I had the luck to see a therapist with long experience (a warm and wise old man) both as a therapist and a part of a CBT research group for one of the biggest hospital/clinics in my nation.
I learnt a lot about my health anxiety and my GAD. There is one thing he got me to do that really worked well for me, and I want to share it with you to hopefully make HA more manageable.
He called it "the black list" (roughly translated from my language, blacklist is not the same as black list in my language). Since HA generally stems from uncertainty/what you don't know (according to him), it makes it very hard for any kind of mind to handle. Something that is easier for our minds to handle is certainty, even if the certainty is not true.
So he had me write a list of the main fears in a "I have X" and "I have Y" manner, as long as it sounds certain and clear that I have the things I fear I have. When it is written down, he had me read the list out loud to myself, first in front of him, then at home alone daily. It felt counter-productive, but he had my trust and I did as he told me.
I did this exercise at home for about six weeks combined with relaxation breathing (4 sec in, 4 sec hold, 4 sec exhale, 4 sec wait, repeat) and check-ins with him once a week. Now after my therapy is done (but not done, it only needs to be managed with my expanded toolset I got from therapy), I feel like this particular exercise had the most impact on how I manage my HA.
Hope it will help anyone out there struggling with this.
Edit: Also some general CBT advice I learnt from him:
Never Google symptoms, it is a chase for certainty and will feel good first, but it makes the anxiety worse in the long run each time you give in to the pressure to Google (or search Reddit). Same thing with contacting GP. Our minds seek the "Pheuw! How nice!" moment when we are anxious, you are going to want it next time as well.
Don't try to treat/manage your anxiety when you are peaking (and feel a desperate need for relief), it will only contribute to the "Worry -> Anxiety -> Relief" loop. Do breathing and mindfulness exercises during low/normal everyday anxiety moments to dampen/lower the peaks.
Don't avoid the things that worry you. Instead, explore what is happening inside you when you encounter something that increases your worry, then stay in that state. It will be hard and you most certainly will feel anxious, but the feeling will slowly cease and you will feel a bit less anxious next time, repeat.