Awaken with rapid heart rate and palipatations

Two nights over the past several weeks I have awakened and had a very rapid heart rate, so fast I can't count, shaking and trembling and heart palipatations.  Also weak feeling and very scared.  I couldn't get it to calm down for about 50 minutes or so.  I tried holding my breath which I've heard will slow down your heart rate and that didn't work. Holding my nose and mouth shut and blowing and that didn't work either.  In reading these posts I've found it could be a number of things.  My dr. told me once that I had a hyperdynamic heart and was very sensitive, especially to adrenaline.  I do have anxiety, but how would a panic attack come out while you're sleeping?  Also I read that sleep apnea could cause you to awaken quickly because of low oxygen levels, but would this cause a rapid heart rate for so long.   Finally it just started slowing down and was over.  The next morning I felt exhausted and trembly.  Any suggestions you could give...This has only happened twice but I'm almost scared to go to sleep anymore for fear it will happen again..Never has happened during the day.

[CCF CARDIO MD JMF]

Dear PD,

I would recommend a full evaluation by your cardiologist.  This evaluation may include a holter monitor to characterixe these episodes.  

While these symptoms may be anxiety and may be a panic attack, it would be important to rule out arrhythmia.