Imagine two big highways on either side of your neck, called carotid arteries, that supply blood to your brain. Sometimes, one of these highways gets a tear in its wall. This tear allows blood to get in between the layers of the artery wall, which can lead to a blockage or reduce blood flow to the brain. That's what we call carotid artery dissection. It's like having a roadblock on a major route to the brain, which can be pretty serious.