@gravelgertie There is no way of telling unless you try a cardioversion. It may just work. It should take only one cardioversion, but each session comprises three zaps with the second and third having successively higher joules. If none of them works, you go home, or remain in hospital if you need urgent care.

An ablation will probably work if the EP finds the correct area to ablate. Sometimes the culprit is the AV node, in which case it may be that you'll need to have it neutralized via an ablation and a pacemaker installed. That's the last option, with ablating another way/place first, or a cardioversion.

Your heart is a muscle. It can get fatigued and/or damaged. So, the wisdom is that you should not tolerate what is arguably 'tachycardia' or a tachyarrhythmia higher than 100 BPM for more than 24 hours. If the problem doesn't self-limit inside of 24 hours, get to an ER for care. If your HR is higher than 140 BPM, it may mean a higher risk of stroke (which I can explain in another post if you're really interested), and you should seek help if it doesn't correct inside of 4 hours.