For a few seconds at least, it doesn’t hurt. The oxygen from my previous breaths lasts a little while. But with empty lungs it doesn’t take long for the suffocating feeling to start.

First it sets the blood pounding in my head. Then my body twitches with the frantic desire to draw breath, my ribcage jerking in a series of desperate hiccups. I don’t give in. The pain centres me, sets the world to rights. It is a show of my love to put myself through this. It’s a way to express the deepest empathy I know.

I count the seconds. Normally I can last no more than thirty.

Today I force myself to forty-two.

I am gasping when I reach the surface. I turn to the poolside, hiding my face. No one has noticed, they never do. After all, I’m only down there for half a minute, not much more. Not time enough for anyone to worry. Most people wouldn’t empty their lungs before going under. The rush of air back into my lungs feels like such a sweet relief, and like a betrayal. I have done it though. I have levelled the balance. Like drawing a thick black line through my head, ordering the chaos of my mind.

I feel so much better afterwards. My head is so much clearer. It’s as though that suffering beneath the water washes away the shame and guilt, and I can be my ordinary, clear-headed self again. Your anxiety, your paranoia, I remind myself, it’s driven by guilt, it always was. I’ve made this link before, but somehow, along the way, I’ve forgotten it. I never quite told the mental health professionals the truth. They had their formulations and I had mine. I – we – never told anyone. But if you address the guilt, I remember now, then all the anxiety melts away.

When I check my phone in the changing room, there are two missed calls and a voicemail from Freya. I simply delete them: one, two, three. She doesn’t need to call me or visit. There’s no reason for her to worry about me now. I won’t be pursuing Sarah’s case any more.

Outside the swimming pool, it’s striking how much better I feel. My damp hair, crackling with chlorine, makes my head sing with the crisp cold, and the air, the sounds, the whole world around me feels clearer, as though cotton wool has fallen from my ears and a film has been washed away from my eyes. I can breathe right to the bottom of my lungs.

The mind is so powerful. Anxious people constantly need proof that things are okay. Normal people start from the assumption that everything is fine.