The light didn't prevent John from sleeping, and the laudanum didn't prevent John from being an idiot. A high idiot, who had no tolerance to any kind of drug, even the cough syrup, much less an opiate. Out of pain, on top? Yeah, he should have slept. He didn't immediate, just drifted in a haze, and watched Ben from under his eyelashes.
Right up until he noticed Ben trying to get comfortable. It took another few minutes for him to move, but he eventually got an arm out from under himself, and grabbed Ben's wrist.