Before take-off, please ensure your seat backs and tray tables are in their full upright positions — and your sinuses are clear.

Otherwise, you may land yourself in ED, with serious consequences.

As with this passenger, who was taken via ambulance after sudden loss of vision in the right eye three hours into a 12-hour international flight.

He had experienced blocked nasal passages and mid-facial tenderness before boarding the aircraft, for which he had been prescribed oral antibiotics and a nasal decongestant by a local GP.