Is this normal???

I'm 29 weeks and I'm a FTM so I still don't know what's normal and what's not normal when pregnant... I've only had this happen a handful of times but it's happening now and I don't know if it's normal or if I need to go get checked out.. I'm just sitting relaxing and all of a sudden my heart starts racing really fast, so fast that it knocks the wind out of me and it's hard to catch my breath.. right now it's been going on for a few minutes I've never had it last this long and I'm not sure if something is wrong or if others experience this too... please help!!!