• ☀ = Lights on or off?

Off. But sometimes, if he is sleeping along side Wrathia, he will give the dim nightlight of fireflies to calm her. Though the sight does nothing for him, he is calmed from seeing her serenity. 

• ✖ = Does the character have nightmares?

Before the titan attack, never. He even reveled in the fact that he may very well be a nightmare for others. But after, he does sometimes, when he finds time to sleep. Fear of becoming nothing. Nightmares of the dreadful attack claiming his wife again. Never do they truly become more VIVID than in his dreams. 

• ❀ = Do they use stimulus to help them sleep? (e.g. candles, music, aromatherapy)

He ‘prides’ himself that he’s a fast sleeper. And a deep one at that fact, but nothing soothes him more than the trust of another person near or right next to him. He is slightly foolish in that way, if someone he believes is his friend, he lets his guard down for them. And thus falls faster with someone around.