Second heart beat?

[Qedies]

So, I'm 20 years old and have no real health problems. I do suffer nightmares very frequently at some periods.

For the last two weeks or so, my girlfriend tells me that she wakes up some nights and finds my breathing abnormally heavy, and something beating hard and fast on the RIGHT side of my chest.

She is adamant that it isn't my heart because she could feel my heart beat as well on the left. I myself have awakened once and indeed, had the right side of my chest beating very hard and fast for some reason.
Anybody have any idea what this is?

[Qedies]

I have had my bp and heart rate checked, both were regular. The doctor just related the intense heart beat to the nightmares.
What she didn't understand was why I felt it was on the right side. But I'm sure it wasn't my heart that was beating, and my girlfriend did say she felt my heart and whatever was beating abnormally hard wasn't my heart, but something next to it.

[Jerry_NJ]

nothing to rally base a reply...but it is never too early to discuss with a doctor.  
do you ave any numbers heart rate, blood pressure, heart rate regular??? so on.