I've Been Experiencing A Feeling Like I'm Nervous Or Anxious

I've been experiencing a feeling like I'm nervous or anxious about something when I'm not. It gives me a butterfly feeling in my stomach and chest but I'm not nervous about anything...just that feeling. It wakes me up at night and it makes my heart race like I'm being chased or scared like in a dream. It keeps me up half the night. When I do fall asleep it happens again and again. I then feel very shaky and sometimes tremble and feel weak. What can this be? Adrenaline surges? GERD? Heart issues?