I'm with Soidhonia -- I never had panic attacks but experienced what you did (but didn't pass out) with just a bad start to a menstrual period, I only had 3 bad ones in my life so it wasn't something that happened regularly or anything; I didn't have pain but had to be helped out of the shower. Physical weakness, mental fuzziness and blackouts don't have to involve the heart necessarily and if you didn't have an attack when on monitors, how can they see/rule out what's causing it?