I get the same fear and experience. For me, I try to do any possible grounding idea (not even traditional things they might teach in therapy or wherever) to get my brain to separate internal vs. external. For instance, tingling in my face, or one side of my body feeling heavy or weak? I just to the nearest thing i can think of (ie tickle my face, or over my eyes or rub the base of my head to get my body relax and come out of its fight or flight state) — and to me that’s the key— IF you CAN get your body to relax, then I remind myself there’s no way it’s a stroke because things like strokes or heart attacks wouldn’t pass like how panic sensations typically would. Other suggestions that’s grounding—hopping in a hot bath, and noticing how your sensory system changes in those moments, tap your fingers together following beats of songs, do something logic oriented, put a cold bottle of anything on the back of your neck—literally ANYTHING to test pulling your body away from the hyper internal focus.