Still Can't Sleep

The heart pounding problem I've had continues. The second I lay flat, it pounds harder and harder. If I turn on my side it gets even worse. If I manage to drift off, almost to sleep, I'm jolted awake by the sensation that my heart has stopped, and I'm about to die. I gasp, waking poor Luke up, my heart pounds extra hard, and I feel like I'm suffocating. It's terrifying and I don't know how much more of this I can take. I'm really at my wits end, and the lack of sleep is really taking it's toll.