I don't know the technical reason why this happens but I do know it happens to people like us. I have found when I'm overtired, this happens more. It also happens more when I'm not properly hydrated. I'm dealing with it right now. I was progressing so well, then found out I'm pg. Kinda not in the recovery plan. So now I feel like I'm taking a couple/few steps back. :( It does get better as you get better. I went months and months without this happening at all.
Hugs and hoping you can sleep well. I know how not fun it can be.
I found hawthorne very helpful in this horrible AF symptom. You lay down to rest and cannot because of your pounding heart. I took whatever brand I could get at my local Vitamin Shoppe -- usually Solaray or Natures Way. I started taking it every day (follow the directions).. before bed. It helped a lot.
Hawthorn berry is THE heart remedy and has been for many, many years. I was taking some for awhile then quit. Thank you for the remind. It can actually heal and repair the heart. It amazes me.