Hi,
I have similar anxiety and claustrophobia issues as you do, not to mention a downright ridiculous fear of anything that cuts or sticks me, so to speak. While I haven't had a breast procedure done (yet), I had other procedures done with sedative anesthetic. Like the previous poster, I had no problems at all during the procedures and apparently actually slept through most of them since there was nothing else to do.
Hope this helps.
I also suffer from panic and anxiety attacks. In twlight sleep you will just be very relaxed and not really care what is going on around you. I found it quite enjoyable. Try to enjoy it yourself. Probaly easier said than done. Keep us posted. You can always ask what meds to use to get you there and post back. It's usually Verased.