I had a serious off in 2016. Over the handlebars. Head into the ground, neck bent back resulting in bruising to the spinal cord and long term rehabilitation. Front of helmet cracked with the impact. Mercifully no head injury to compound an already very serious situation. I, for one, believe that small piece of polystyrene had a significant role to play in the lack of a head injury.
I had a serious off about 8 years ago, when I was returning from work along the Colwick Loop Road cycle track and a pedestrian who'd been looking in the opposite direction suddenly ran straight across in front of me, still looking in the opposite diresction, and totally ignoring my shouted warning. I braked hard and tried to swerve around him, but just clipped him with the left side of the bars. He was spun round and fell to the floor relatively unscathed; my front wheel pringled and I went over the handlebars, pivoting on my right forearm, with the bike going over my head. I ended up on my back, with feet pointing in the direction of travel, and the bike and panniers several yards further forward.
If I had been wearing a helmet, my head would have hit the ground and bent my neck back, resulting in (at best) bruising to the spinal cord and long term rehabilitation, at worst a broken neck and death or tetraplegic injury.
Mercifully no head injury, as my head didn't make contact with the ground; I walked the remaining 4km home with my bike balanced on the rear wheel, bleeding from the right forearm and a few abrasions on my left knuckles.
After a couple of days, my right arm was black from wrist to shoulder, but I was back on my bike commuting to work again, after a day on the bus.
I, for one, know very well that I wouldn't still be posting on this forum if I'd been wearing a polystyrene hat.