I'm super stressed out and have horrible anxiety. I worry about everything. After I had my daughter three years ago, it got worse. Every now and then for a week maybe 2 days at a time, my heart will beat really fast while just standing, until I sit down. I also feel strain in my tummy, neck, shoulders and back. I sometimes even feel nausea with a headache. I've had tests run on my heart and things seem fine. What's going on? I'm miserable.