shortness of breath and rapid heart beat

[twiggy45]

Hi,I'm 45 years old and for the past 10 years off and on I have experienced episodes where my heart will beat fast. At first it was just a rapid heart beat but over the past couple years it has escelated to where I will feel short of breath and have the rapid heart beat. I have had many tests over the years. EKG's, holter monitor, ultrasound and most recent was a nuclear stress test (March 07) which came back normal. I finally ended up having my daughter call 911 this last time because I really felt like I couldn't breath good and my heart was beating fast and kept skipping beats. It always happens at night (middle of nite) but I can go a few months without it happening. I just dont' know what it could be if all my test come back normal. I'm not overweight (actually probably a few pounds underweight) I'm 5'6" and weigh about 117 pounds I've been thin my whole life. Also my cholesterol is in normal range and bloodpressure is usually around 114/80 although when the paramedics took my bp it was 132/80 but obviously my body had just been under alot of stress so it was bound to be higher. Can someone please tell me if they experience this and any suggestions. I think most dr's think it's anxiety or panic attacks but why wouldn't' I have them when I really feel stressed. I do have stress in my life but how come I wouldn't have them constantly and why the shortness of breath?... I'd appreciate any feedback.... Thank you!