Hi Sarah,
My daytime panic attacks have disappeared, but now I have nightime panic attacks, bad ones, one or 2 times a week, where my heart races. Mild ones every night when I just have fallen asleep. Thankfully, they never last long however.
Nothing to worry about your heart, but if your heart is racing, say over 100 beats for too long (like an hour) see your doctor about it. My doctor told me a way which actually seems to work. Try holding your breath and pushing out as if you were trying to blow out of your mouth or your nose or through a closed straw, putting pressure on you sinuses. This should slow the heart rate down, it affects what is called the sympathetic nervous system (your heart has to slow down if it doesn't get enough oxygen). I know it's hard by try not to panic when your heart is racing, think to your self it will slow down eventually. This train of though really gets it back to normal quick for me.
Guido :)