One case was when this man lived in Minnesota and it was very icy, he just got done grocery shopping. He was bringing things inside, and he slipped and fell on his front stairs broke his arm, and cracked his skull open. But nobody found him till his wife got home so he also got hyperthermia. When he got to the hospital he go put on life support. The doctors said he was in a deep coma. He never woke up. That's how serious comas are. One slip and fall to the head can change your life forever.
When in a coma your brain activity can become very depressed. Which means that it's basically the same type of depression as when you're awake. But when sleeping your brain tells itself to be sad because you are doing nothing and feel like you have no one there. The doctors can diagnose that statement with MRI’s and CT scan. There are many ways to tell what you’re brain activity is or what's its doing.