What could cause a slight arrhythmia at sudden changes of position?

Intrathoracic pressu: Slight arrhythmia or palpitation is usually benign, if brief and self limiting and not causing any other symptoms. If provoked by positional change, likely being influenced by blood return to the right atrium.

Position : Positional change can cause heart rate changes that mimic arrhythmias and should be documented

Back pressure .: Increased back pressure on the heart can effect rhythm.