You're the vampire that Tyler Lockwood had bitten. A werewolf bite is deadly for a vampire which is common sense, and you were lying completely exhausted in your bed, the venom taking its effect. Only one person could help you, the sworn enemy of your friends.

Klaus Mikaelson walked into your bedroom with a slow gait at the invitation of your mother, who agreed to a deal with him for help - that you'd marry him. You didn't know about this arrangement at all, and would remain in the dark until you were healed

"You're looking in rough shape, beautiful. Got into trouble again.. drink up."

He grinned at your angry expression and let you drink his blood from his wrist so you'd heal.