I get this still with some things, my health anxiety used to be worse. Recently I've been having shooting pains in my skull and that's created a worry about a brain tumour. My way of getting over it is this:
Is it a brain tumour? Ok, it might be a brain tumour although the likelihood is that it isn't. I've had lots of weird, real sensations before where I thought it was something serious and they went away. Sometimes our bodies do weird shit for no reason! That's just a part of living in an extremely complex machine with millions of processes and chemical reactions happening every second.
When I've felt weird stuff before, what was it? When I think about past weird sensations I've felt, these have stopped when I've been feeling less anxious. Therefore my anxiety is probably causing these symptoms, or at the least making me notice things that I would usually shrug off.
Is it good to worry about it? Does worrying about having a brain tumour help me? Is it going to make a brain tumour go away? Will the worry make treatment of a brain tumour better? Will worrying make it stop? If I got diagnosed tomorrow would I say 'Well thank goodness I was worried about it all this time!'? No to all of the above. Ok, so it is serving no purpose, it's not helping in any way, and in fact it's making me feel pretty shitty.
So what are my options? I suppose I can accept that there might be a small chance it's a tumour. This is the number 1 thing I've learned. It's to say 'Ok mind, I recognise and I've noted down that there is this anxious thought and there may be some truth to it. I'm not ignoring it, but I'm not going to give it all my attention right now because that's making me feel like shit.'
Anxious thoughts feed off attention. If I just say 'Ok yes I know you're there but right now I'm not going to worry about you', they go away. And then weeks later I'll realise that huh, I haven't felt that weird pain in quite a while.
Which is exactly what's happened with the shooting pain in my skull. It was with me for months and now I haven't felt it in weeks. Sometimes our bodies do unexplainable weird stuff.
I hope that helps, it has definitely taken practice to get this far, but I have felt much less anxious for a long while now.