Later Merlin would blame his hangover on why he didn't flinch away from Zach's touch; as it was the hand on his back settled him in a way that the hangover potion hadn't, even if it was for a moment.
He almost nodded to Zach's offers, especially for a drink (he loathed being sick and everything that came with it, especially the vomit-mouth afterward) but he had more pressing concerns before that, most specifically, "What am I doing here?" he couldn't even find the energy to sound suspicious; he was just glad his visions were backing off for the morning.