Tightening in abdomen and then can't breathe?

Okay it just started tonight. I was laying on my side in bed and I felt my little girl moving around as usual. And then it almost felt like a rolling sensation or something and my abdomen got really tight and then it's almost like I couldn't breathe. My body tingled and then I could finally breathe again. It happened again just a few minutes ago. What exactly is happening?

It's not painful or anything. My entire belly felt hard internally and then it's like my lungs were being squished.

And now I'm short of breath.

Also, what do Braxton hicks contractions feel like? Are they painful? Not painful? I'm sure I'd know I was having one if I knew what they feel like.

I'm only concerned because the weird tightening and short of breath thing has happened twice.

I'm 20w5d