Getting out of bed on the wrong side is now a scientific fact of stronger reliability than the existence of the Higgs boson, according to a study of 3,000 people that we report today. Those who sleep to the left of their husband or wife are more likely to be cheerful and positive and can cope better with heavy workloads. Yet these cheerful left-liers fear that their mood would turn nasty were they to sleep on the right. Indeed, reluctance to swap sides is one of the few unamiable characteristics of this happy breed. What this discovery of Galilean import does not reveal is whether the grumpy migrate to the right or have grumpiness thrust upon them nightly by their disadvantageous bedtime position. Clearly, there is an urgent need for far more research on these nocturnal dispositions. It must be a wake-up call for our finest scientific minds.