I had this same problem and it was finally diagnosed as GERD, which is basically acid reflux. Some people experience it as heartburn but I never did and I experienced it as panic attacks instead. What happens is that when you lay down, stomach acid backs up into your throat where it doesn't belong. The body feels acid burning the tissues and has a fight or flight response which basically is a panic attack, except that you cna get one every night. Getting back out of bed helps because when you're not laying down, the acid is no longer backing up into your throat. Losing weight is also known to help a lot with GERD. Stopping alcohol consumption helps GERD too.   I didn't believe GERD was the cause of my bedtime panic attacks, which I always worried were heart attacks, but my doctor prescribed a GERD medicine for me and my panic attacks stopped, so he was right! Might be the same for you.