From Sarah Waters' The Night Watch:
The house was perfectly dark after that, and the darkness, and the silence, made Helen feel worse than ever. She had only to reach for the switch of the lamp, the dial of the wireless, to change the mood of the place, but she couldn’t do it; she was quite cut off from ordinary habits and things. She sat a little longer, then got up and began to pace. The pacing was like something an actress might do in a play, to communicate a state of despair or dementedness, and didn’t feel real. She got down on the floor, drew up her legs, put her arms before her face: this pose didn’t feel real, either, but she held it, for almost twenty minutes. Perhaps Julia will come down and see me lying on the floor, she thought, as she lay there; she thought that if Julia did that, then she would at least realize the extremity of the feeling by which she, Helen, was gripped.
Then she saw at last that she would only look absurd. She got up. She was chilled, and cramped. She went to the mirror. It was unnerving, gazing at your face in a mirror in a darkened room; there was a little light from a street-lamp, however, and she could see by this that her cheek and bare arm were marked red and white, as if in little weals, from where she’d lain upon the carpet. The marks were satisfying, at least. She’d often longed, in fact, for her jealousy to take some physical form; she’d sometimes thought, in moments like this, I’ll burn myself, or I’ll cut myself. For a burn or a cut might be shown, might be nursed, might scar or heal, would be a miserable kind of emblem; would anyway be there, on the surface of her body, rather than corroding it from within. Now the thought came to her again, that she might scar herself in some way. It came, like the solution to a problem. I won’t be doing it, she said to herself, like some hysterical girl. I won’t be doing it for Julia, hoping she’ll come and catch me at it...I’ll be doing it for myself, as a secret.
She proceeded, now, as if she’d planned the entire operation in advance. She opened the neck of the sponge-bag and drew out the slim chromium case that held the safety-razor she and Julia used for shaving their legs. She took the razor out, unwound its screw, lifted off the little hub of metal, and eased out the blade.
She was left with two short crimson lines, such as might have been made by a hard but playful swipe from the paw of a cat.
She sat down on the edge of the bath. The shock of cutting, she thought, had produced some change in her, some chemical change: she felt quite unnaturally clear-headed, alive and chastened. She’d lost the certainty that the cutting of her leg was a sane and reasonable thing to do...And, yet— She kept looking at the crimson lines, in a half-perplexed, half-admiring way. You perfect fool, she thought; but she thought it almost jauntily. At last she took up the blade again, washed it, screwed it back beneath its metal hub, and put the razor back in its case. She switched off the light, allowed her eyes to grow used to the darkness, then let herself into the hall and went up to the bedroom.