It depends on what the arrhythmia is, how fast the heart rate is, and how long it has been going on. Short runs lasting several minutes and then reverting to normal sinus for hours is not so bad...certainly not urgent. However, there are a couple of arrhythmias that are bad and you don't want them at all if you can help it, even for a few minutes. Those are ventricular fibrillation and ventricular tachycardia. Arrhythmias like premature atrial complexes (PACs), and PVCs, and atrial fibrillation, or SVT (supraventricular tachycardia) are benign when in the early stages and when they self-convert after an hour or so.

However, any arrhythmia lasting more than 24 hours with a rate above 110 BPM is cause for concern and, yes, you would then get yourself to an ER quickly. It can tire the heart.

And yes, it is common, especially for AF sufferers, to have their hearts act up when they get into bed and relax for the night. My sister-in-law has this problem. I haven't heard that PACs also do this, but I suppose each case is different.

For you, apart from not wanting an arrhythmia of any description...at all..., doctors will want to act when you tell them you're feeling distinctly unwell, even if you're mostly just anxious and are not able to sleep. Tell your cardiologist about this, or at least a family doctor or GP.