(NBC) -- If you've ever taken a blow to the head you know how scary it can be. It could even be life threatening.
Sandra Berry travels up and down the same stairs every day. A few months back a stumble on the steps lead to a serious injury.
"I went down on my knees and my head slammed into the wall," she recalls.
Sandra didn't think much of it and proceeded to drive into town to pick up her husband from an appointment.
When she started falling asleep back at home, her husband took action taking her to the emergency room.
That simple bump on the head had caused a subdural hematoma, bleeding between Sandra's brain and skull.
"Older people are at risk, because most of them, or some of them, are on blood thinners and those can incraes the risk of bleeding even with what would be considered a fairly minor injury," explains neurosurgeon Dr. Scott Sanderson.
Sandra was on blood thinners which made her injury life threatening.
Dr. Sanderson only had minutes to perform a craniotomy.
He removed a piece out of her skull to access the injury and stop the bleeding.
"If you get to peopel fast enough it's exceedingly effective," he says. "It depends on how bad their injury was when they got to see us."
People in their 60s and older are at risk for this type of injury.
Babies during the first few years of life are also at high risk.
Warning signs include nausea, vomiting, feeling sleepy and slurred speech.
Then there are extremely dangerous symptoms in the pupils of the eyes.
Right before patient dies their pupil dilates abnormally.