phyxius,

I was watching a lecture recently where they explained that the brain has a system of regulating blood pressure to just the brain. This system is often damaged from a head injury. Second Impact Syndrome is a result of this system being damaged and another impact occurring before this self-regulating system heals. The resulting over-pressure in the brain can cause quick coma and even death.

Taking your blood pressure on your arm is not necessarily related to the BP to your brain. The body will shut down blood flow to all but the brain in an attempt to survive an injury. This same system can malfunction. Other than a Doppler UltraSound of the carotid and vertebral arteries, I don't think there is a way to check this system.

btw, a Doppler UltraSound of the carotid and vertebral arteries is simple and painless. I had one done to check for vertebral arterial insufficiency. About $300 full price.