Quote Originally Posted by SerLuke View Post
They’ve previously said that dragon’s come from another star not another dimension, I think the question is more how they got their to our star since I’m assuming their wings aren’t enough for interstellar travel
Midgarsormr is a borderline god-like entity, so I don't think interstellar travel posed much of an issue for him.

It's been stated that he fled his homeworld with the eggs of his offspring (Thanks to Omega, who was implied to just be the latest in a series of attacks from some highly advanced civilization) who eventually became the progenitors of all dragonkind on Hydaelyn.