Desire might well tap you on the shoulder in the early stages of a relationship, but the hormones that fuel the tapping disappear after about 18 months. However; plenty of couples find desire lowers dramatically after about nine months.

But don't panic. It doesn't mean you'll never fancy each other again; it just means that you need to keep reminding your body and brain how much you enjoy sex. Spontaneous sex is usually good sex. But planning a sex session — anticipating it, looking forward to it — this makes for pretty good sex as well.