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I was travelling down from the 10th floor of my office building in the lift when I bent over to fasten my shoelace. I was suddenly dizzy and disoriented and had to kneel down to stop myself falling over. I never have any difficulties travelling in lifts, but presumably this was in some way caused by the fact that I was descending. I tried it again a week later with much the same effect. Why does bending over in a descending lift make me dizzy?

• It is not uncommon to feel dizzy in a lift. This is a symptom of motion sickness and occurs when the brain gets conflicting messages from the systems regulating balance and spatial orientation: vision, the vestibular system in the inner ears, and the of receptors in the muscles and joints.

The vestibular system comprises the otolithic organs, which detect linear acceleration, and the semicircular canals, which detect rotational movements – pitch, roll and yaw.

When you stand in a descending lift, there is a conflict between vision and the otolithic organs. This is enough to disorient some people and cause motion sickness. If a person bends over, there is also conflict between vision and the semicircular canals. To the semicircular canals, the act of bending is exaggerated by the lift’s descent, which is not detected visually. This is like walking towards the prow of a ship along an internal corridor as the ship pitches into a trough. This could have been your tipping point (in more ways than one) into mild motion sickness.

“If you bend over in a lift, there is conflict between vision and the semicircular canals that detect pitch”

If you were to bend over in the descending lift and, at the same time, shake your head from side to side, it would induce aspects of roll and possibly yaw, depending on how far you were to bend. This would cause further disorientation and increase the likelihood of you landing on your head.

David Muir, Portobello High School, Edinburgh, UK