It doesn't take long. Damon knows it's going to happen before it does. He makes no move to leave or to run.

Bonnie is angry with him. She's feeling a lot of emotions. They are all helping to power her witch-y abilities. He doesn't really stand a chance, and it's not like he's trying to fight it, to get away. The first time she did it she wasn't trying very hard. He had a hand to his head as the pain ripped through him, but this? This is something else altogether. It's clear she's been practicing. It's clear she wants to hurt him. It means he's brought to his knees with a sound of sheer pain quickly.

He hits the ground, doubled over, as his mind feels like it's being torn to shreds.