Arthur said nothing and waited for Merlin to stumble out of the bathroom before unstopping the drain and climbing to his feet. The amount of space between their rooms was exceedingly limited, less, in fact, then when they were home, but that didn't stop Arthur from following Merlin as stealthily as he could. To make sure he didn't trip over and invisible bump in the carpeting and break his too-thin neck.
The fact that it was a very real possibility was sad.
Hugging the open door, he leaned out into the hall, reassuring himself that Merlin would in fact make it into his own room before passing out again.