The dilemma I’ve been with my partner for nine months and everything about the relationship has been great – bar one thing. The sex has been wonderful, but she has a thing about wanting me to spank her. At first I laughed, as I thought it was quite an odd request. But it was clear she was serious, and this is where the problem lies. I have spanked her a few times and, though it arouses her, it makes me feel guilty. I feel bad for all sorts of reasons. But I wonder if I’m overreacting: she is far from submissive in day-to-day life and, as she’s said, it’s her choice. This is a difficult subject to write about, and I don’t know if others have similar concerns. I want us to be able to enjoy sex without anxiety, and would appreciate your views. It’s not something I’ve been able to talk about with anyone.

Mariella replies Don’t worry! What might seem odd, kinky and guilt-inducing to you would be quite low on any list of deviant sexual peccadillos. If sex only boiled down to the bare necessities we’d live in a much less exciting world. Slapping, biting and other forms of mildly masochistic fun are not a majority choice, but you’d be surprised how often they feature as an element in carnal pleasure. That’s why the word “consensual” is the most important one in any lover’s dictionary.

Individual pleasure is as diverse as any display of individuality from food to furniture, clothes to pets

I’m not sure there is such a thing as “normal” sex; instead, individual pleasure is as diverse as any display of individuality from food to furniture, clothes to pets. That’s why compatibility is such an important element of any relationship. The positive thing about your current union, despite the scruples you’re experiencing, is that your girlfriend feels comfortable enough with you to articulate her desire. There are many reasons why such an act could be a stimulant for your girlfriend and only a small number of them would qualify as deep, dark, distasteful and worthy of analysis. In sex, as in dreams, we are often hostage to forces and urges that we don’t understand and can’t explain. Sometimes it takes a request like your girlfriend’s to discover an act that excites you too but also the reverse can be true and that’s when you need to be honest about how it makes you feel.

There’s no need to feel guilty and uncomfortable about spanking in the heights of ecstasy if it gives her pleasure and doesn’t cause you pain. There is also no compulsion for you to indulge in actions that you don’t feel comfortable with. The right to choose is paramount and should preside over all our individual actions. What two adults decide to do in the privacy of their own space should really be up to them but let’s also admit it’s where sexual politics can get very complicated indeed. Bringing acts of violence, however small, into the bedroom is a choice you need to make with your head, rather than the parts of your body more involved with copulation. It’s too easy for behaviour deemed acceptable in the height of ardour to change image when lust is no longer the driving emotion between you. Beware the disgruntled lover if sex games have escalated to harder-to-rationalise heights, and always make sure you’re both enjoying the activities. There’s no accounting for tastes and a pretty distinct boundary between unwelcome abusive behaviour and a mild spanking at your partner’s request. I had a girlfriend once who used to joke about her penchant for “light strangulation”, which I found completely baffling. Personally I’ve no wish to push myself closer to the final curtain every time I have sex but there’s clearly a market for that action out there also.

One of my favourite documentaries is Fetishes, Nick Broomfield’s foray into an S&M parlour and the matter-of-fact way in which the participants discussed their bizarre proclivities in such everyday fashion. We live in a great big glorious melting pot of different desires, and every now and again we rub up against someone with whom we share similar tastes. That’s when sex can be at its most exciting but also it’s most troubling, leading you into a crepuscular world where your instincts are your only guide. You’ll get plenty of beard-strokers with theories about why we find such peculiar things titillating – Freudians are particularly expansive on the subject – but sometimes it is just the expression of a physical desire that has no traumatic precedent.

That’s the trouble with rules and regulations about sex: an approved list of dos would be unlikely to include slapping, however light, but you’re not the first person to have been asked to perform such admonishments. It seems barely worth spelling out but we are complicated organisms and our physical desires don’t always sit comfortably in a tidy graph of acceptable behaviour. If you’re uncomfortable with living up to your girlfriend’s requests you must say so, exactly as she has an equal right to express her own no-go areas. Removing slapping from your love-making could see her eventually move on to someone happy to indulge her mildly masochistic tendency, but conversely she might compromise with more “wholesome” sexual adventures if she’s found the right man. Ultimately, the only influence on your decision should be what you’re comfortable with.

• If you have a dilemma, send a brief email to mariella.frostrup@observer.co.uk. Follow her on Twitter @mariellaf1