I checked with various doctors upon my return. Ear doctor: no inner ear barotrauma. Brain scan: everything normal. However, a painful endoscopy of the heart discovered a slight deformation of the membrane between my left and right ventricles, which under high pressure could have released the passage of micro-bubbles, from one side to the other. This would apparently have affected the brain, inducing vertigo. Happily, it fixes itself in time, given no exertion – shh! Since then, no further symptoms.