What happens next?

How to identify atrial fibrillation
Monitor any breathlessness you experience.
When your heart starts beating quickly, as it does when you have atrial fibrillation, the rest of your body gets less blood supply because your heart is beating less efficiently. When your body's blood supply slows down, oxygen levels in your blood decrease, which will make you feel like you can't catch your breath.
You may experience this feeling of breathlessness when you are climbing the stairs, exercising, or simply just walking. Notice if you feel like your heart is pounding.