Dave - perhaps the only reason your neck was sore was that the extra 2-3cm of material on your head, combined with the slightly higher mass, caused your head to make contact with the ground when it otherwise wouldn't have. Perhaps, in fact, you're incredibly lucky to have got away with a minor neck injury, when a more major, possibly neurologically-compromising, one was on the cards as a result of you recklessly wearing a helmet?
Don't get me wrong - like so many on here I'm anti-compulsion rather than anti-helmet: I'm a risk-taker, so I wear one almost all the time on a bike.
"Helmet saved my life" stories, though, and their variants annoy me a little; they are likely to be nonsensical given that there is significant statistical evidence that populations without mandatory helmet regulations do not suffer massively higher head-injury levels than those with. That is not to say that helmets aren't useful[*] - just that if most of the "Helmet saved my life" stories were true, we'd see a massive death toll among those that choose not to wear them. That huge death toll appears to be missing...
[* for, among other things:
- mounting a camera;
- with a peak, for keep some sun and rain from the eyes;
- butting branches out of the way when on the mountain bike;
- generating interesting hairstyles, post-ride;
- protecting the head when bashing it against one's desk;
- stopping doctors and nurses from tutting if one has to go to hospital.]