Anxiety is exacerbated during times of stress. Covid is placing unprecedented stress on all of us right now. Getting a vaccine and then hearing it "may cause myocarditis" can be very stressful, and we lose the ability to internalize the caveat that it's attached to a 0.004% incidence rate.

Anxiety also causes you to perceive normal bodily sensations, that you otherwise filtered out, with heightened sensitivity.

"With health anxiety there is the misinterpretation of discomfort and normal bodily sensations as dangerous. The body is very noisy. Healthy human bodies produce all sorts of physical symptoms that might be uncomfortable, unexpected, and unwanted, but not dangerous." https://adaa.org/learn-from-us/from-the-experts/blog-posts/c...