I don't think there's any danger to fly, but you still may feel pretty beat. I was up and out on day 2, but spent it locally in my town and took it easy for a few days before returning to my normal routine.
The other thing you will no doubt have is a sore groin/upper leg. If you have a lot of walking to do around the airport terminals, this may be difficult for you. I limped around for about 2 weeks following mine. Go easy!
From the USA? Well at least it isn't the 13th, still I think a too aggressive and optimistic plan... but discuss with your doctor, who I will guess will say either "no" or "it depends".
You didn't say what type of ablation, not all ablations are equal and not all patients are either.
Best to delay one of these activities
Good luck.
I've had 3 ablations and felt pretty good within a few days and certainly by a week. But I don't know how comfortable it would be to fly within 2 days. The groin area tends to bruise up pretty well (even though I'm female I wore boxers and loose pants) and it can be uncomfortable to sit for any length of time. Occasionally a person will develop a hematoma at the puncture site and that feels a bit worse.
Any way you can shift the flight to a few days later? Then again, if you're just going from UK to Germany, that's probably a quick trip. If it's less than 2 hours, it probably won't be any trouble.