I'm wondering.........how old are you? Are you anywhere near perimenopause? (Can start in the late 30's). This has happened to me, and others who were going through perimenopause. I used to have panic attacks every night. I would wake up with a gasp, and feel like I couldn't breath and my heart would be pounding. Female hormones can do funky, funky things to us!
Also, I wanted to ask.......how does your doc know you don't have apnea? Did he do something like a oximeter test on you at home? He can't know you don't have it, unless he's tested you for it. I have sleep apnea, as did my father, so I'm wondering if it runs in families. There is obstructive apnea (from the tissues in the back of your throat closing off), and Central apnea, which is caused in your brain.
Are you on any meds?