I had almost the exact same thing happen with my friend! Her saddle slipped while cantering and she hit her head hard. I think she was knocked out for the few seconds it took for me to pull up my horse, leap off, and run to her. She wasn't quite as vocal as your friend, she was very quiet while walking back to the barn, and after I got her inside, every five minutes or so she would ask where she was ... I thought she was going to die, I was terrified. She went to the hospital, came home and slept, and was better the next morning. To this day, there are significant gaps in her memory of that day she fell off.
I'm glad your friend went to the hospital. I'm no expert but I know that a concussion as major as that definitely needs to be looked at, there's so much that can go wrong with a brain. I hope your friend is ok, lots of hugs to you!
"When the power of love overcomes the love of power, the world will finally know peace." - Jimi Hendrix