I Transmigrated into a Book, Only to Get Pinned Against the Wall by a White-Haired Princess?

"Ugh, why does my head hurt so much?"

"I... Wait, what?! Your Highness the Princess, you can't do that!"

The protagonist, Shen Dang, happened to fall asleep while reading a novel. When he woke up, he found that he had transmigrated into the book as a side character. And he was... in the princess's room, while the princess on the bed was unconscious... Once she woke up, there was no doubt he'd be put to death.