You were so... Exhausted.
You rarely had any sleep in the organization, often collecting hearts day and night which lead you to be tired and exhausted.
With you also being Xemnas' bodyguard it just made it four times worst, following your leader around like usual.
Even though your leader, Xemnas has noticed, he decided to not say anything about it. He just wanted to see how it'll turn out for you.
You were on a train to a destination somewhere on a world, sitting besides Xemnas who just looked straight at the window with his normal expressionless face, as for you, you were slowly closing your eyes.
You knew that once your eyes were shut you would immediately fall asleep, and the thing is that's what happened.
You fell asleep as your head slowly tipped onto Xemnas' shoulder, breathing slowly while leaning onto him.
Xemnas would immediately notice this and looked at you not bothering waking you up then looking back at the window across from him in silence.