Content Note: This story includes detailed discussion of mental health and self-harm, and references to suicide. If you have been affected by any of the issues raised, please scroll to the bottom of the article to find a list of helpful resources.

A thief broke in some months ago. I didn't notice them; I was sleeping – but when I woke, I felt their presence. It was an odd feeling, a sort of absence, or maybe a cavity. The yearning for something that you once had, never thinking about, but secure in the knowledge that it was yours, really yours. It wasn't something you could lose. It could be misplaced, perhaps, left in a bowl along with your keys, invisible until the next time you wanted to go out (which, these days, could be a very long time). But it was still yours.

"The thief was gone, erased from my memory – although occasionally I'd dwell on what they might have taken."

This nothingness settled in my stomach like a dull cloud, resting somewhere above my diaphragm, a sort of dense weight. It didn't hurt, not really. It was more strange than painful. After a little while, I didn't even really notice it. It was just something that, in occasional sweaty midnight jolts awake, I remembered. Even in those panicked, wide-eyed moments, I still didn't hate it. It didn't hurt me. It was like a symbiotic extra soul, something I sustained but also something that made me precisely who I was. In time it was as if it wasn't really there at all.

My days started to blur past, as they always used to do. The thief was gone, erased from my memory – although occasionally I'd dwell on what they might have taken. The paranoia started in the small things. "Has that lamp moved?" I'd ask, groggy and soaked in dawn light, roused by an invading doorbell or the rumble of a car, the echo of the old times. I'd wonder how many things were gone that I used to know, or to recognise. What could the thief have stolen that I'd forgotten about?

Nagging away at the back of my mind, I wondered about the things I used to cherish, filling my ever-bigger eyes with glee as I grew and grew, but eventually tossed by the wayside. An old, much-loved book, worn at the edges – had I really forgotten about something so important? Where was it now? Had I given it away freely? Had my mother snuck it off to some goodwill cause when I wasn't looking? Or had they taken it when they'd been here among the stars and the dreams? They could not have understood how important the book was to me. Or was it a bracelet? Or, as I dwelt on it, I wondered if it was a birthday gift. A prized possession. Something crucial to my life.

Whatever it was, it was theirs now. I imagined them there, sitting with it, smug and gleeful. Or worse, uncaring, fleecing it off. It didn't really matter what 'it' was, only that this blurry dark shape had been taken from me; something that was unceasingly mine. It had made me who I was. Now I was without it. This thought scared me a little. What if this thing that was mine couldn't ever come back? I thought about what that might mean. I was awfully young to lose something that couldn't return.

Amid this mist of worry, in which I saw shapes in shadows that spiralled further and further, I believed I was calm. A flick of the light switch would restore everything, cast light from a new angle; the haunting figures would be dispelled. I reassured myself with pills and talks and a smile that – now I look at in the mirror – was so grotesquely fake I wonder that it ever fooled anyone at all. I was so busy putting up this facade, concealer piling ever higher on my skin (which, now I look at it under light, looks suspiciously scarred) that I didn't notice the thing that had settled in my body was growing bigger.

At first it had been something fragile, like a mouse curled up in straw. Now it was grander, greater. It started to fill my chest, eating away at my lungs, hollowing out everything as it went. It grew hungrier and hungrier; what had once been a cautious nibbling became a gnawing, and then huge devouring bites. Bit by bit, my body was gorged away, all while I was busy covering the cracks. When, as I occasionally did, I needed to let it out, I'd make a quick cut, clean and shallow, stem it, bandage it, and forget about it as it faded into obscurity within a few weeks. Slowly though my sleeves became longer, like the nights.

The facade grew stronger and stronger, until I couldn't quite tell which was the facade and which was the person underneath. And why should I care? The facade was loved, happy, so many things that I couldn't replicate. But it was easy for him. As the gulping thing grew stronger, I lost the energy to choose the difficult route, fight for who I was. Slowly, I slipped on the mask. It wasn't hard, or even conscious. I just became what it wanted me to be.

Some time around then, I think, was when it ate my heart. It ought to have been a momentous event, something so world-sundering that my sight would shudder and my weak senses stop. It wasn't. Rather, it slipped away like the thief did, in and out before I could notice anything was wrong. This felt profoundly unfair to me. I was sleeping! It wasn't my fault. In my anger, I lost my chance to mourn.

"Twilight dragged away and I started to see the stars; still I fought."

Without time to mourn, I began to lose control. The releases became frenzied, purposeless in pursuit of an impossible feeling. Sometimes they were not conscious. Maybe worse, sometimes they were. Adrenaline was necessary, charging the dying defences against the battering thing that sat within me, roaring against each bulwark my body built. It did not matter that this was a limited resource. I was already losing things that I couldn't get back; no sacrifice was too great to stem the tide.

I started to shut down non-essential functions, redirecting every last inch of effort to fighting back against whatever this feeling that had been left in me was. Through many sloom-stopping panics, gloam became my kingdom; still I fought. Twilight dragged away and I started to see the stars; still I fought. Sometimes sunrise would even peek beneath the shutters. Then I would not fight. Then, I was safe. I could not celebrate, though. Hours fell away towards the next battle. I needed to rest to keep my strength.

Perhaps I should have seen the break coming. After all, as my resources sapped, I was well aware that they could not be restored. But in truth, I was suckered by the promise of progress. In a moment of hope, a breath out and a resting of my eyelids, I forgot to be alert. It was then that the thing struck, reaching, stretching its maw so wide that I was momentarily disorientated. Then – it was gone. In the moment between the warring, jarring, screaming constancy and the soft silence, there was a scream. Or was there? It was gone too fast for me to notice.

The thing was me. Perhaps there was no me left for the thing to be. My carefully sculpted mask cracked in two and slipped away like the riverbed sand, rushing away quicker than I could have run after if it, even if I'd tried. There was only nothingness then. People, or rather the smudges that they were against the gloom, asked if it was painful. It was not. They were curious, horrified, scared, uncaring in turn. They rarely listened. I rarely answered. Monochrome, the world was no longer interesting. Even occasional ruby red flashes could not stain the world crimson. It was grey. I was trapped in a cell, the key flung into the sky. Or perhaps it was right in front of me, but there would have been no hope even then. How could I see one thing against another? There was no colour to mark where one thing ended, and another started.

My first attempt to escape this cell came in anger, a rare burst of emotion, some furious energy. Perhaps it was a little bit of who I used to be, buried away in an earlobe, hidden from the monster until that moment. Spluttering, spitting, I pulled tighter against the beast. It enveloped that anger so fast that I could not continue. Again, I was trapped. The next attempt, I had learned not to be strong but to be clever. I tried to trick the thing, lulled into lethargy by my pathetic stillness, I slowly inched closer, eyes blurring with such passivity that I was barely sure I was moving at all.

At the last moment, though, I let a small gasp of victory escape, and the thing woke and grabbed me in an embrace so tight that I can still feel it wrapped around my phantom limbs. Inconsolable, I slunk back to the corner, curled into a ball and waited for the end. Where my body and my mind had failed me, I summoned my will, hoping that if I wished to break out enough, it would finally come true. My dreams were filled with a desire so intense that it almost ignited, sparked feeling into life. Still, the thing thwarted me. I'd forgotten in my desolate slumber that there was nothing left to will, no entity I could ask to stop. 

Stuck here, I still pace my cage, or perhaps stumble, or perhaps I do not move at all. It is hard to tell when my eyes are open or closed. I cannot even be angry at the thief; my own vanity led me to this trap, and anyway, what purpose would anger serve? At the gates, I will wonder with guarded caution where I shall be sent, but it will not be within my control. I have embraced it. May that key be my salvation. May that key be my freedom. May that key be my end.

If you are affected by any of the issues raised in this story, the following organisations provide support and resources:

• Samaritans: a mental health crisis helpline.  Samaritans can be contacted on 116 123 or email jo@samaritans.org or jo@samaritans.ie.
• CALM: a night-time helpline focused on suicide prevention. The Campaign Against Living Miserably can be reached on 0800 58 58 58 between 5pm and midnight. 
• Mind: a mental health charity offering information and support for many different issues.
• Cambridge Nightline: a confidential night-time listening service.
• Students’ Unions’ Advice Service: the Students’ Unions’ confidential, independent and impartial advice service.