Did the monitor capture one of the nocturnal events? If not, you may want to talk with your doctor about wearing an event monitor. It is worn for a longer period of time and you can "record" activity as it is happening. You are probably just fine, but I always like to know that the doctor SEES when I am describing when it comes to my heart rhythm.
I have a medtronic device inplanted because they weren't able to find my source of tachycardia (they have since found it). I took some times wake up with a pounding heart. I decided to record it with my device to see what it was the next time I had my monitor read. I had a 3-5 beat run of PVC's, which the cardiologist said nothing to worry about.
I WOULD LOOK INTO PERI MENOPAUSE THAT COULD BE SOMETING TO DO WITH IT HORMONES MAKE MY HEART GO CRAZY!
It sounds like I have identical symptoms that you have waking up at night with rapid/irregular heart beats and they are severe. This has been on going for about 15 years; I'm usually dreaming and I awake and the symptoms are so severe I wake my husband and we start to head to ER but it always settles down before we get there. It is so frustrating and I have been to dr. after dr and they can't seem to pinpoint it. I was told I have sinus tach, but they say it is abnormal in that it only happens at night and never during the day. I would really like to get to the bottom of this. I have just spent 3 days in hospital doing eeg recordings to see if that would show us anything.
Not to offer a diagnosis, but you might want to google something called 'noctural panic attacks.' The way these things manifest themselves is apparently *extremely* different from what we normally think of as panic attacks, but palpitations are part of the picture. Here are a couple of links to the condition:
http://web4health.info/en/answers/anx-panic-night.htm
http://www.mayoclinic.com/health/panic-attacks/AN01760/
Have you ruled out sleep apnea as a cause?