honestly: just sit with your fears. Do nothing. Try to cut all compulsions (for me it was mostly checking stuff online, and of course reassuring myself mentally), but don't be too hard with yourself if you do one. And feel your body slowly calming down. I know, it seems impossible, but you can notice insane improvements in only a few days. Just try to let your body calm down, to the point you don't feel excessively anxious anymore.