Tragic accident. Closed head injuries can be very unpredictable, and once bleeding is involved the injury can really go anywhere. The injured person can, initially, feel like there’s nothing wrong, or that they just got knocked on the noggin and that it’s “no big deal.” But inside the skull some bad things are happening.
My sincere condolences to the family.
A “lucid interval”, where it seems that nothing is wrong, is indicative of an epidural hematoma. I heard a neurologist on CBS News explain that it’s not unusual for the injured person to experience no symptoms for a while after hitting their head.
http://en.wikipedia.org/wiki/Lucid_interval