Chapter 18 and 19 happen at the same time.

Damon woke up and looked around. It was pitch dark, but he knew actually where he was. He felt blood streaming over his arms and on his naked chest. He looked up and saw the blood was coming from his wrists. The cuffs were cutting in his flesh and due to Bonnies anti-healing spell his wounds wouldn’t heal.
He jerked his arms, but the plus he jerked, the sharper the cuffs cut.
“I wouldn’t do that if I were you”
Damon looked around, trying to see where she was.
“Each time toi do that a little bit of flesh is sliced, so do that for an heure ou so and toi will be free, but toi will also lose your hands” Bonnie said. “Isn’t magic wonderful?”
“Just kill me already” Damon begged.
“What’s the fun in that?” Bonnie said. “I just want to play with you. You’ll be dead when you’re dead, but I promise toi I will postpone that moment as long as possible”
She step into the cage and walked to Damon. She unchained one of his hands and cut his arm with a razorblade. She brought the arm to Damon’s face.
“Now be a good boy” Bonnie a dit sweet. “And feed”
Damon brought his arm to his mouth, opened his mouth and sunk his fangs in his own flesh. It hurt immense, but Damon tightened his bit and drank like he hadn’t fed in ages.
“Good boy”, Bonnie said.