Pain in my chest:

Last week I was sleeping, and my husband woke me up to tell me something and as I sat up, my chest felt like I had someone sitting on it. I don't have any medical conditions linked to my heart or lungs, and I'm in the medical field, so I have a decent understanding of symptoms. It began getting worse and worse until I thought I would pass out from not feeling like I could breathe for the pain and tightness in my chest so I had him take me to the emergency room. After a 45 minute rushed drive there, not 5 minutes before we get to the hospital, it just stops. No pain, no pressure. Nothing. It's as if nothing was ever wrong. I played it safe and still went, afraid it would come back to haunt me if I didn't. She was kicking the whole time, no signs of a heart attack, they did numerous test including an aorta scan on my legs to check for DVT/clotting, an EKG, basic blood work, urine sample, and fetal monitoring. They didn't find anything but a bladder infection, and sent me home with Macrobid. This happens again exactly one week later, I get half way there and it just stops. I've spoke with my OB, which gave me no answers or advice, stating it could be heartburn. I had severe acid reflux as a child, this is waaay beyond that kind of pain. Nothing I've found triggers it, whether that be food, emotions, sleeping or awake, activities, or overall health.  Has anyone had this sort of pain or experience before, and if so what was your diagnosis and treatment?