I promise this relates.
Sherlock Holmes' sleep patterns are erratic at best. His roommate's are perfectly regular, with one notable exception:
Nightmares.
Holmes is not asleep in his room. He hears each scream each night, screams of pain, of sorrow, of guilt, of anger.
He wonders each night whether he ought to awake the doctor, soothe him with the idea of dreams being only that, of the ghazis and blood and desert being the past; he reminds himself each time he is barely acquaintances with this fellow, and army men tend to have terrible pride.
Only after Watson's staunch loyalty shows itself does he enter the room and do his best.