Sleep on your back? Turns out you're a „dominant leader with a need for control". Sleep curled up like a fetus? Tough on the outside, sensitive inside. Psychological tests and the whole Freudian questionnaire industry look at that theory with boredom and have stopped believing it. And yet, articles on „sleeping position and personality" pop up every season.

The six traditionally cited positions - fetal, log (on the side with arms down), yearner (on the side with arms up), soldier (back with arms at the body), stomach, and starfish - get different attributions in pop psychology. „Logs" are „relaxed and social", soldiers „disciplined and reserved", stomach sleepers „anxious and nervous". Sounds good at a cocktail dinner, but doesn't hold up under science.

Clinical psychologist Montserrat Guerra is blunt: „Conclusions about personality drawn from a single specific behaviour, like sleep position, aren't very reliable." That's the underlying problem with the whole personality „quick test" industry - you take one variable and build a whole conclusion on it.

What actually determines sleep position? Comfort. Back or neck pain. Temperature. The type of mattress. A partner who occupies more than half the bed. Those factors are always stronger than any „psychological tendency" - that has been studied in a string of sleep-quality studies, and the results are consistent.

Still, something in this story pulls at us. We want to believe that even in the unconscious state, the body reveals something about our internal life. And maybe there's something to that - but not in such a literal sense. If you change positions often at night, you're probably tense about something. If you sleep solidly in one position, you're probably tired or stuck in a routine. That's all. It's not a „psychological portrait", just a simple biological reaction.