Wife punched and slapped my 3 year old at 3 am

My 3 year old woke my wife up at 3 ( don’t know why) and my wife , in a fit of rage , punched and slapped him in the face until i restrained her. Son’s nose started bleed from this. I know she loves him but I am scared. She was not able to sleep for a few days prior but this is not what should be done. I sleep in other room but my dad instinct told me to check on my son and when I opened the door , wife was hitting him. I am scared and need help. What should I do. via /r/Parenting http://bit.ly/2VQOnBh