I have the same symptoms. When I am falling a sleep, I wake up scared cause it feels like my heart has stopped and I can't breathe. I finally went to my Doctor and did some blood work and I found out that I have Hashimoto Thyroiditis. I did some research and the symptoms are the same that I have. I hope this helps everyone. Please have your blood work done checking your TSH, T3 and T4 and also your antibodies.