He growled at his brother for dropping Justine's name on him but he had a point. If he woke up ravenous it wouldn't be good but he hated leaving and having Harry stay behind with the vampire to watch his back. Molly he trusted to put herself in danger for him but Phae was still on his watch and don't trust list.
"Watch your back damn it." He closed his eyes and deliberately gave in to the worry and near panic from the first dream and his need to know his brother was all right. Like he said he was a nervous sleeper. It came from years of worrying his father or one of his enemies was going to have him killed at any moment.
It meant when he was afraid he jerked awake and went on guard.