I had something very similar. For me it would happen right when I was on the verge of falling asleep. I would get to the point where I was just about to cross over into sleep and get hit with a sudden jolt of adrenaline and anxiety. My heart would race and I would be up for another few hours and then the process would repeat through the night. I would also get hit with panic attacks during the day as well but not nearly as many as in the night. It was awful. They did go away however. I still get anxiety and I’m 19 months into this thing but it’s way less than it was during that period. One thing that helped was after that jolt of adrenaline I would listen to ocean wave sounds on YouTube and time my breathing to the sound of the waves. I know it sounds kinda stupid but it would help me calm down way faster. Not sure If this is exactly what you are experiencing but I hope it helps.