For so very much of his life, Erik could not bear to sleep. Not that he thought sleep was a waste of time, mind, or that he would be far better off if he used the time normally reserved for sleep for other duties, such as composing or sketching or reading or contemplating a more efficient way to kill someone. Rather, sleeping necessitated nightmares which in turn led to him losing sleep. For decades it seemed he lived in a state of perpetual exhaustion.
In Persia the opium brought him some relief, gave him nights of a sleep that was not particularly restful but was at least without nightmares. Then came the decision to replace opium with morphine for the sake of his voice. He could not say he ever felt well-rested, though it was sleep and for that he could not complain.
Then Christine Daaé came into his life. For the first time he had something to dream about that was not awash in blood. His dreams left him tormented, his heart aching for to hold her, yet the nightmares were held at bay. Still, he was not rested. In fact, it left him more tired than ever, so tired that he felt he could lie down, close his eyes, and never rise again.
Then Christine Daaé returned to him, swearing to become his wife. She could not marry the Vicomte, she said, too much had changed and if Erik would still have her... He agreed on the spot, and they were married before a priest that he scared out of bed for the purpose and who likely thought he himself was dreaming.
They did not make love that first night, nor any of the nights that came in the first few months. He thought of it, more than once, but he was far too afraid of what she might think if she would see him, all of him. But with her at his side, sharing his bed and nestled close to his side, he was not afraid to dream, in fact welcomed his dreams so shrouded where they in her.
They are still shrouded in her - her kisses, her voice, her softness. She has not driven the nightmares away completely and he strongly suspects that nothing ever will, but they are only an occasional inconvenience now, albeit one that wakes him sweating. Nor will he ever be able to give up the morphine. To do so after all of this time would kill him. The shock would overwhelm his already-battered heart and stop it, though he grants that the morphine itself will likely someday do that just as easily with the difference that it will have prolonged his life.
(He prefers not to think of such things. It feels as if he might be defiling his mind.)
Now, though, he can sleep again after his nightmares, because Christine will hold him close and sing to soothe him, and he rather thinks he might die without her, or at the very least go truly insane. But she has vowed that she will never leave him, so help her, God, and in her arms, her soft voice singing lullabies, it is safe to sleep.