A few times. Once more than 60 years ago - can't remember why.

Once aged about 20. In a crowded Central Line tube. Probably the result of a couple of pints of beer after giving a pint of blood, but I blame the lack of ventilation on the tube.

A handful of times over the years - at needles. Mostly the dentist, but the most recent 2 years ago at the epidural for a hip replacement.

Three mystifying occasions over 3 months the winter before last. Once driving, twice at concerts. Sitting each time, plenty of warning (so the driving was OK) and only out for seconds. Dozens of tests showed nothing.

Phil