A Japanese method promising sleep in ten minutes sounds like one more internet trick you have already seen. This time there is a book behind it - "Yoga for Sleep" by the instructors Mariko and Tomoya, founders of the popular Japanese yoga channel B-life - and logic that is harder to dismiss.

The idea is not to stretch until you are worn out. The idea is to switch on the parasympathetic nervous system, the one that tells the body it is allowed to stop standing guard. Under constant stress the body stays permanently on alert: quickened pulse, shallow breathing, a head that will not stop calculating. The exercises are done in bed, and they require no prior yoga experience and no flexibility whatsoever.

The first is the turtle pose. Soles together, knees opened into a diamond, spine lengthening on the inhale, then the body folding slowly forward while the hands hold the feet. It releases tension in the lower back, opens up the hips and has a calming effect.

The second is the half-knot. You sit with one leg extended, the other folded across the body, spine straight, then lean slowly forward. It helps with back pain and makes the breath deeper and slower.

The third is not even a movement. The body scan: you lie on your back, arms slightly apart, palms up, and move your attention from head to feet, noticing what you feel - without grading it. Plenty of people fall asleep before finishing the routine.

The rest is staging: pyjamas, dimmed lights, music if it helps. None of this costs a cent and none of it asks for a subscription.

The most provocative part is not the yoga. It is the assumption that a sleep problem is physical rather than circumstantial. If your head is running at night because tomorrow you have a real worry, no turtle pose is going to pay that bill. The method helps you calm the body - but it does not pretend it will calm your life. That is honest. Most advice of this kind isn't.