Coming above ground at Kings Cross this morning, I took the steps two at a time, wincing as my rucksack bounced against my back. No matter how carefully I pack my bag, somehow a spike heel always ends up digging into the small of my back. Never mind the spanking – when I get home from a shoot I’m much more likely to be bruised by shoes.

The shoot is with Punishment Bitch, one of the Lady Sonia group of sites. Sonia herself is a slender and self-possessed woman in her prime, with eyes that are impossible to look away from. We drive to the studio and talk shop.

Studios are odd places, never inhabited but constantly striving to seem real. And yet real things have happened here, real conversations, real spankings, real sex. It doesn’t count when the cameras are rolling but the ghost of it lingers; studios have a feel similar to school playgrounds, clamouring with the echos of the humans that fleetingly spent their time here.

This one takes up the top floor of an old building. Mouldy sofas and dry, rusty washbasins punctuate the long climb to the top floor. The walls of the stairway are peeling. Inside, a space that could be a glorious loft apartment is messy and thrown-together, mismatched rooms chopped in amongst each other. Inflatable sofas compete with disembodied enamel bathtubs; an Edwardian parlour is tucked away beside a stable reeking of two-year-old hay bales; graffitied walls float from the ceiling, connected to nothing. You don’t ever want to lie on the beds.

I make tea, we joke and laugh about the studio, Sonia and I get ready. I relax. Once I’m working it’s easy, I know what I’m doing. There’s something scintillating about shooting that never gets old no matter how many times you do it. The silk stockings and the fetish heels make me feel sexy, and I’m working with a woman who is effortlessly glamorous. The director doesn’t need a story for the spanking but we, the actors, the women, do: we come up with one between us, and enjoy the sarcastic, erotic banter even if none of the viewers do. Our characters are competing for power over each other and it becomes a game of wits, culminating in a punchline. At this stage it’s mostly “sensual” pattycake spanking and the improvisation is more exhilirating.

Soon, though, our minds and my bottom are warmed up, and we start to connect, the dialogue becomes more convincing and our body language starts to sync. She whips me with a riding crop and I hiss between my teeth at the sudden panic of hurt. Breathe through it, remember you can do this, remember this is what you’re being paid for, don’t you dare wimp out now. Whimper, remember that crying out helps, let myself squeal at the next cutting stroke. Sonia mocks me for that – “you felt that one, didn’t you?” – and that helps too. I muster my courage and struggle my way through two more strokes before my body finally catches up and a slow wave of endorphines settles over me like a blanket. Mellow now. I arc to meet each stroke. When she stops, I don’t want her to.

On the train home I squeeze my legs together, remembering my wetness at the end of that last scene, grateful that they were professional enough to spare my blushes and not comment. There’s a sharp line between my exhibitionist self on camera, willing to be exposed and shamed, willing to be seen to enjoy it, and my professional self off camera, laughing and wry and determinedly disengaged. Ironically, the closer the trust and connection with the models I’m working with, the more inclined I am to keep my two selves separate. I can flirt as much as I like on camera, be as aroused and helpless as I like, because I can trust them to not think it’s real. Which liberates me enough to make it real, but not in a way I’m prepared to share. This is my own enjoyment, and it’s a blessing and a curse.

Lust torments me all the way home. By the time I reach my front door I’m drained and exhausted. My phone has run out of battery and Tom’s meant to be coming round tonight but I don’t know when and maybe he won’t. The endorphine crash leaves me listless and melancholy. I spend a little time relieving the ache that has been building since that session with the crop, and afterwards I weep at stupid things and mope around the house getting nothing done.

Then I pull myself together, make some tea, and give myself a stern telling-off for (yet again) not predicting the endorphine crash and looking after myself properly. I should know by now to have chocolate in the house after a shoot. Lust gives way to exhaustion, and when Tom arrives I won’t know whether to tear my clothes off and throw myself at him, or curl up in his arms and demand cuddles. I want to be whipped again, I want to share some of the spark and energy from today’s shoot with my beloved, I want to offer some of that energy to him. But I’m physically drained, and connecting with my real boyfriend when half my head is still being whipped by Sonia is always difficult to navigate.

I’ve done this so many times, and I’m still not used to it.