...I believe total mental shut down is crucial, early on. Like immediately. Once a concussion is diagnosed, stop doing anything requiring mentation for 2-3 days. No school, no reading, no tv, no computers, no phone/texting, no gaming, no running, no sports. Sleep if you want, listen to soft music, but just rest the mind. I find that recovery is much faster, rather than trying to push through it.

Someone who needs a dark room years later is probably someone who has a much more serious injury, or perhaps didn't do proper recovery immediately following the original injury.