Is it normal that my friend got stabbed and she doesn't know how

My friend woke up one morning and as she was going into the shower she realized that her neck was bleeding a lot. She tolled her mom and her mom immediately took her to the hospital. The cut is around 2 inches wide. The doctor tolled her that if it would have been a little more deep it would have cut something and she would've died.

When the doctor asked her what happened she tolled him she did not know . He thought she did it to herself . But I know she did not . There is no proof of any type of weapons that were found in her house not even around her bed.

They have not figured out what could have prevented this . Has anything like this ever happened to anyone ? What could have caused this?