As Dark mentions the phrase 'pulled me out,' Strange can't help but wince. It's obvious from that wince that he knows more about the idea of the Mirror pulling something out of someone. But how best to explain it...

"In all likelihood, the Mirror you saw is the Silver Mirror. It's a fae artifact of immense power. The Silver Mirror has the power to banish the Light or the Dark from one's self." The way Strange talks, it's obvious those nouns have capital-letter levels of importance even if he can't actually speak the capital letters in what he's saying.

"I don't know what happened to you. But I suspect it's the reason why you don't remember what happened or how you got here."