What's pain is unfathomable, and where exactly in the body is that pain? How big is it? Where are its edges? How long does it actually last? How does it move and change? How bad would it be in comparison to something like hitting your shin on a coffee table (in theory, don't actually do the experiment ;). Is there actually real danger or just imagined danger? Can you notice the thoughts as just fleeting experiences? This sort of inquiry is one approach.
However, it might not be the right approach. Feelings of being overwhelmed by Fear can be the Fear stage of insight, which arises in context and sequence with the other stages, or it might be something else, even psychosis, paranoia, standard anxiety, an overactive imagination, evidence that there is trauma or depression to be dealt with first, or something else like that. Those diagnoses very well might benefit from other approaches, as outlined in resources such as Trauma-Sensitive Mindfulness, by David Treleaven, which I recommend you read, as it might provide helpful clues, and, if it resonates, you might seek the benefit of the guidance of people who know how to handle that territory well.
Best wishes,
Daniel
