Why could your heart flutter when you wake up?

Arrhythmias. Fluttering in the chest can be a sign of cardiac arrhythmias, but it does not have to be. Frequently, people present with this complaint, have a heart monitor placed, report heart fluttering on their monitor's diary, and have no arrhythmias recorded on the monitor. Nevertheless if an arrhythmia is suspected, the first diagnostic tests should be a heart monitor and thyroid function tests.