Hi!
Just wanted to offer a different perspective...
Crohn's disease can cause low potassium (because of diarrhea or inability to properly absorb nutrients), which can lead to heart palpitations.
Another thing to look at would be how much you are eating during the day. If you are chronically under eating this puts stress on your heart, especially if you have a very low BMI and your body is so starved that it catabolizes muscle and basically "eats away" at the muscles -- the heart is a muscle. I only point this out because I know that with CD it can be uncomfortable to eat sometimes and many people have a difficulty meeting their needs. It is kind of out there (this kind of situation occurs frequently in very progressed anorexia nervosa), but it's definitely something to keep in mind.
Ultimately, we can't tell you what it is...go to the doctor!!
Although I shouldn't be speaking, I get heart palpitations too