Dear Allison,
Sounds like what happened to me when I was first diagnosed with panic disorder - I was constantly checking my pulse, waking up in the night not being able to breath, hyperveniltating and, having chest pains. That became the telling factor in my prognosis and, now, a constant in my life. They discovered I have an MVP, which is a Mitral Valve Prolapse - this explained everything - research this strange little heart quirk - many people with panic disorders have MVPs. I am now taking Ativan - this has been the only drug over the years to totally relieve me of panic attacks - I have 'break throughs' when my life is very stressful in one way or another, but, if I take my meds like clock work, all is well.
I hope that helped,
Maria