What’s the most terrifying 'We need to leave... now' gut feeling you’ve ever had?

As a teenager in England, I had to deliver mail from the city council to various locations around the city. I had a delivery to make to an office block. I arrived at what I thought was the correct office block, but it looked deserted. I headed up the stairs to the second floor and found the office I thought I needed to make a delivery to. I opened a door to see the entire floor was empty, no desks, no chairs, just a huge entire floor of carpeted office space. In the middle of the floor, about fifty feet away, sat a guy tied to a single chair. Two men stood on either side of him. For about five seconds we all looked at one another, then I turned and bolted out of that building and didn't stop running until I got back to my workplace.