Why can't I stop thinking of catheter and endoscopy and stuff?

I have s fear of these kinds stuff and simillar. I can stop thinking of it for like3 weeks.. but then it comes back and i stsrt thinking lver and over... i just have fear.. i also think how on earth did i get my 4 wisdom tooth out same time.. i did
Why can't I stop thinking of catheter and endoscopy and stuff?
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