Re: Hard Fall, feeling rough.
Bicycle helmets are designed to break up even in impacts that would not have hurt you-- it's how they absorb energy, and it's good business for those who make and sell helmets.
The amount of energy absorption required to certify a bicycle helmet is designed to make a very specific event nonlethal: the head of a standing adult falling from that height to the ground. No speed added, no moving car added, and no helping push from the rest of the body. It can help in a modest impact, but it ain't much. Don't fool yourself into believing it's more protective than it is.
Our granddaddies and great-granddaddies fell off their bikes and hit their heads too-- some of them while riding high-wheelers. Most of the time they came out OK, just like most of the time we do too. Head injury rates and fatality rates among bicyclists have not dropped significantly since bicycle helmets came into broad use, which I think is as good a measure as any for how effective they are.
Wear it if it makes you feel prepared, but don't let it make you feel safe. It's just not that powerful. The brain inside is a much more effective safety device.
"When I see an adult on a bicycle, I do not despair for the future of the human race."