This is just my 2 cents but it sounds like you're just perpetuating a feeling you could have had once and then feared so it happens again and again. You can think about it subconsciously and then bam! You suddenly think of that horrible feeling and it comes back again. It's not really a panic attack or depersonalisation in my opinion, but it sounds like it really depends on your fear of it. You're not going mad, I promise. Anxiety never causes insanity, it just feels that way sometimes :) that's all it is though, just a fear and a thought. Next time it comes on, turn your reaction around. Welcome it, ask for more. You'd be surprised how well this works for people. I know it might seem scary at first, but fighting it isn't working, so you've got nothing to lose. I really think it's something you are perpetuating because you're afraid--when you take the fear away I'm sure these feelings will go too :) the meds will help too, especially bwith physical symptoms.