Hemingway wasn't called a Potions Master without cause; seconds after drinking the potion, Remus felt his body relax, the pain dulling as he took in a deep breath of air. He drank some of the water as well, the cool liquid feeling strange as it slid down his throat and caused an unexpected soreness in his esophagus, but he knew it was for the best, and he took it quietly.
His eyes suddenly felt very heavy, and it was a struggle to keep them open long enough to take one last look at Sirius. His hand found Sirius's, and he squeezed it again as he sighed a "Thanks" softly, slipping into unconsciousness.