i have had more than one time being awakened by my heart beating like i just ran a marathon. what causes this?

I have been awakened several times with my heart being like I just ran a marathon.  When I awoke I was laying on my side, heart beating wildly.  I turn over on my back and it slows down.  I go back to sleep and it happens again and wakes me up.  I just got off a 30 dya heart monitor, nothing happened.  I have no memory of any dream or anything that scared me.  I rarly dream at all.  I am an insomniac and take restoril.  I have long laundry list of health problems and am currently deemed disabled.  I get maybe 1 good nights sleep a week.  Can anyone tell me why this happens?  Or better, what it may be?

[Steven Y Park, MD]

Your condition definitely sounds puzzling. It sounds like you have positional tachycardia, worse on your side. It sounds like a heart issue, but since you do complain of sleep issues, seeing a sleep specialist may be an option if your cardiologist can't help you. Good luck.