I cant breathe

So I'm laying down trying to sleep and I have such a hard time breathing so I'm tossing and turning. Adding pillows to elevate my upper body. Nothing is comfortable. So I get up and sit for a lil and while I'm just sitting up I notice my heart rate increases and I start feeling really faint and lightheaded. My question is, is that normal?? When should I be concerned? I'm only 24 weeks so this makes me concerned for how much more ima grow which will make it harder for me. I honestly want to go to er because it scared me but idk if I'm being dramatic.