This incident happened to me a long time ago. Each time I tell this story, it only reinforces my faith in the maha-mantra. When it happened I have not met my Srila Gurudeva. Even then the maha-mantra can protect and save you.
I once had a colleague who was a pretty good dresser. She's also quite a looker as she gets all the attention from the boys in the office.
One fine afternoon, I was sitting right opposite her cracking my head as I was suffering from writer's block. She (let's call her Sherry) started to shiver. My initial reaction was the air-conditioning was too cold. Besides, everyone was almost down with the flu at that time.
Soon my other colleagues scooted her off to a room adjoining to our main writers' room. The poor girl was really sick, I thought. I continued doing whatever work since there were others looking after her at that moment.
All of a sudden, my colleagues started running out of the room. Their faces looking quite blank. I tried to stop them to find out what was the matter. None answered me. It was as though I did not exist.
I then ventured to the back room. I saw Sherry lying down and crying.
"Why did they have to do that. Leaving her alone. Poor girl!"
I was like really DUH??!!
I asked Sherry whether she wanted a blanket or a hot drink. She was shaking now.
She simply said, "I am feeling really, really cold."
I then bent down to check on her temperature. That's when she cried out, "Help me! Help me! It's coming inside me! Help!!!!!!"
It just struck me that she was possessed! Her face started to twist and she snarled at me. Sherry or whatever that was laughed hysterically.
At that moment, (being a real scaredy cat that I am), I kept reciting the maha-mantra.
I pushed her down commanding the thing to shut up and get out of that body.
Giving a haunted laugh, "Sherry" started to push me over. My back was facing an open window in that room. Luckily, that thing wasn't strong enough or else I would have been pushed out of the window and would not live to tell this story today.
It was a battle between the possessed and the sane.
While all this drama was going on, not once did I forget to chant my maha-mantra.
After some time Sherry started to calm down. Crying she said she wanted to go home. I ran out of the room to look for help.
By now my boss had called her family. Soon they arrived and took her home.
Months later Sherry came back to work. A much calmer person.
So what saved me that day? Nothing but the maha-mantra. Never every stop chanting no matter what.