There are also concussions that occur for reasons other than direct impact. In these cases, a helmet is not likely to help you no matter how well it's constructed. I'll still assert that if the fall was in fact "slight" that this couldn't have happened.

"Rotational force is key in concussion. Punches in boxing deliver more rotational force to the head than impacts in sports such as American football, and boxing carries a higher risk of concussion than football"

As for whether I would be dead or not if I hadn't been wearing a helmet, no one including me, can ever prove that. I can only say that, upon examining my helmets after both events, I was glad that I was wearing one.

I also know that I rode like a lunatic as a teenager, and the thought of wearing a helmet never crossed my mind; I'm not even sure they were available back then. If you've ever been to Europe, you'll see many more people riding bikes without helmets than with them. Do what you want.