Two years ago, 63-year-old Paul Bolding was on holiday in Croatia, visiting a beach on a tiny island with his wife, Kirsty. They decided to go to snorkelling, taking turns to go in the sea while the other one looked after their stuff. Paul had a swim and then dozed on a beach mat on the pebbles for a while. When he woke up he had no idea where he was or how he got there.

Not surprisingly, Paul was very scared. His wife took him to sit in the shade, desperately trying to find a way to calm him down and to work out what was happening to him. She told me in Radio 4’s All in the Mind that she soon worked out that he wasn’t able to form any new memories because he kept asking the same questions: “Do you think I’ve got sunstroke? Do you think I fell asleep in the Sun?” This happened more than 20 times.