iPhone 5 HD voice / noise cancellation is weird

I didn't realize what the heck was going on, but while i was driving in the car and talking on the iPhone, I started feeling a strange intense head pressure. It was like head pressure you feel in a plane. I thought there was something wrong with me. Come to find out that this is an iPhone 5 feature. I've used noise canceling headphones before and have felt ear pressure, but this was uncomfortable head pressure. I think there needs to be a setting to shut this off. Has anyone else experienced this? It will only kick in when there is actual noise to cancel, hence why I experienced it while driving.