heaviness in chest

I'm 24 weeks pregnant and earlier today I was laying down on my left side, kind of elevated and started having Braxton hicks. Suddenly my chest felt extremely heavy like I needed to take deep breaths and my heart was pounding. I've never experienced anything like it but I figured maybe it had to do with the BH. Well now I'm laying in bed on my left side again, no BH but I'm having heaviness in my chest and pounding heart again. It's a very uncomfortable feeling and kind of scary. Has anyone else experienced this? Should I call my doctor tomorrow?