Hi Jen.
I had heart palpitations, too. I still have them, ever since the pregnancies. It was worse if I laid on my left side. If I can remember correctly, the doctor said it had something to do with excess blood that your body makes when your pregnant and laying on your left side would make it worse. So I avoided that ! I had them through all 3 of my pregnancies and I survived each one of them without a trip to the cardiologist. After my last baby I went back to work and was still nursing. I had an episode one day where I was palpitating constantly for about an hour. Freaky! So I went to the ER and they put me on a monitor- everything was fine. They told me to rest.
However, now that I'm pushing 40, it makes me a little more unsettled. Recently I started waking up with my heart racing in the middle of the night. So I went to a cardiologist a couple of weeks ago. They did an EKG and I wore a halter monitor- mainly because of family genetics, and I had racing heart AND a history of palpitations. Again, everything turned out fine.
I know it is scary and it still freaks me out on occasion. But every time I have it checked out, I'm fine.
My gut feeling is that it is when I'm very tired and dehydrated (it was worse when I was nursing). So make sure you are drinking a lot of water and getting rest. Also, sleep on your right side at night. The cardiologist has determined that my racing heart was from acid reflux, causing me to feel like I'm suffocating in my sleep and I wake up having a little panic attack. He put me on something for my stomach, and the racing stopped. So I also think that palpitations may be gastreo-intestinal related. But I'm no doctor! That's just my gut feeling.
Good luck!
L.