Fox'a relationship with sleep is a complex one. Often he works late hours, seeing to an administrative side to commanding The Guard. This includes delegating patrol routes, communicating with the CSF and the Special Operations units, as well as case filings and assignments. This takes up much of his time when he is not performing other duties, not leaving much time for sleep.
When he does sleep, though, he’s a light sleeper. Environmental noises he tunes out, and will sleep like the dead through storms. However, if someone were to open the door to his quarters, he would instantly wake. This happens frequently, as Coruscant never sleeps. Our poor commander often finds himself tired, which contributes to his somewhat crass attitude.