When is it too late to have a brain scan from a fall if you think you have a concuccion?

Within 2 days: Optimally, you should get a head ct within 1 hour of the head injury, but as late as 2 days there may yet be utility in ruling out life-threatening hemorrhage. After 2 days, you can certainly get a head ct scan, but it will be academic: if it could have killed you, it would have done so already, so there is nothing the scan would show you that would need to be remedied.

Concussion invisible: Concussion is invisible on a brain scan. Any injury to brain structure, such as a contusion, may show even if the scan is obtained a week or two later. If in doubt, have your doctor examine you first to see if there is anything amiss. If your physician thinks your symptoms require a scan, go for it (it may show things such as delayed bleeding (subdural hematomas) etc. ).