What should I do if my atrial fib intermittent?

See your cardilogist. An intermittent atrial fib can be dangerous because of its unpredictability.
Depends. Possibly nothing but it depends on how often and severe it is. The main issue is rate control meaning the prevention of it going fast. There is also the risk of stroke prevention as that is one of the major concerns in Afib and is treated with anticoagulation. There are are all things to discuss with your doctor.