Psychotherapy helped me. The Jungian idea that anxiety is a message from the unconscious and that often unresolved grief lies at its core.
There’s a book The Wisdom of Anxiety by Sheryl Paul that explains this too, that anxiety will manifest as various different ways (health, relationship etc) but it’s the message underneath that matters. She has a website and Instagram and often talks about health anxiety.
Health anxiety can be trying to divert your attention away from feelings that seem too scary to feel. (To feel health anxiety maybe feels more doable - the mind thinks the big, responsible doctor will help you and fix it all!) but really you will survive feeling the scary feelings and you’ll be able to find a way to parent yourself through it.
Owen O’Kane is really good too, he has so many practical tips on his Instagram and published a book on anxiety recently.
Basically it was abandonment issues and unresolved grief at the heart of it for me. As I’ve grieved my dad never being in my life (working through the anger, fear, loneliness etc) the anxiety has gradually lifted. It helps having a psychotherapist to point all this out to you and sit with you while you feel it all.
CBT and thinking tricks only take you so far with health anxiety I think - in my experience anyway it was a really physical experience (tight throat, panic attacks, feeling like I was going to faint) rather than thought processes. Which was a pain because I’d already spent several years in psychotherapy mastering my thoughts by the time health anxiety gripped me!
Also some pills helped a bit with panic attacks, (pericyazine) I was supposed to take one when I felt a panic attack coming on. But couldn’t always predict them well, and I would feel totally wiped out after the pills, so not ideal.