Transmigrate to Another World and Become a Demon King

When I opened my eyes, I saw an ancient-style bed and house. What was going on? Hadn't I been injured in the war? Why wasn't anything hurting? I got up and checked my feet. I wasn't missing any limbs. And, uh, these clothes were strange. Were they ancient clothes? Man, it's so hot. Where is this place? Wait... wait... wait. Why am I lying in a hospital bed? Where am I? Did I transmigrate? Impossible. That's not scientific. I refuse to believe it. Just then, someone pushed open the door. It was a maid dressed in ancient-style clothes. Seeing Shangguan Ling, she said, "Young Master, you're finally awake! You've been unconscious for seven days. Madam and Master have been so worried they can barely eat. Are you feeling unwell anywhere, Young Master?"