Kate
It could be atrial fibrilation. That's what I have. Mine lasts up to 4 hours sometimes. If it doesn't last long or happen often, I wouldn't worry to much. But the danger from it can be either heart attack (fairly rare) or stroke because the blood pools in the atria and form small clots that then break loose and travel. It is a very common problem. Because mine lasts so long they put me on a beta-blocker and a blood thinner.