I'm 25 weeks (tomorrow) My doctor told me not to lay on my right side because it slows bloodflow to myself & my baby. & that laying on my left side was the best way for us to recieve blood. But whenver I lay on either side my heart starts racing really fast & I lose my breath. So I usually just spend the night sleeping on my back. I'm not sure if it's something to worry about or not, but I figured someone would know why it happens or what to do. Thanks guys !