I get those exactly! It feels like a rush that starts in the middle of your chest, like the feeling you get looking off the top of a tall building, no racing heart, not panicking, just adrenaline rush. Sometimes after Ive fallen asleep I will have one during my sleep that will turn my dream into a nightmare and I will wake up with that surge feeling. Does it shoot through your arms and legs, or just chest area? If mine are strong enough it will send a shooting feeling through my forearms and calves. Recently I saw an endo who put me on thyroid meds, it made me have the rushes every night, she said it sounded like a classic panic attack and that a lot of people with anxiety get them just before they dose off.
I have those and I believe that it is just anxiety..probably because they are in your head before you try and sleep. I will either jerk out of my sleep..sometimes like my brain is jumping..or I'll get this buzzed rush that goes through my body or over my scalp or whatever. The only time this happens is when I'm laying there thinking about how I need to sleep and I hoep i'm not sick, etc.