When I was nine I was frogmarched to the opticians for my first sight test. It was after copying down the fact that “Marco Pob was a famous explorer” from the board at school.

The optometrist explained what the test entailed and asked me questions about how much I watched TV and used computers, all in this incredibly soothing, soft-spoken voice. When she lowered the lights and used the pen torch to see into the backs of my eyes, I experienced this tingling sensation. It began at the crown of my head and trickled over my scalp, down my neck and across my arms and legs. It was so relaxing I could have fallen asleep, though that wouldn’t have been conducive to an eye examination.

About two years ago I found out that this sensation had a name and then realised I also experienced it when people played with my hair in junior school or when I would hear people type on a soft keyboard.

‘Head orgasms’, meditation and near-death experiences