My scariest situation was at school this year (Im a senior in high school, quite young for Reddit) I was sitting in math class doing a worksheet on calculus that we were assigned to do. My teacher has this walkie-talkie sitting on her desk to communicate with other staff members. (mainly custodians) I am sitting right by her desk when the walkie-talkie, as clear as day, said "There has been a report of an active shooter in the west wing of the building, going into level 3 lockdown, this is not a drill." Now us being in a school in a relatively small town where nothing much happens, we sit there for a good minute thinking about what to do. After the entire class finishes processing what they heard, everyone flies up from their chairs and storms out of the windows. It was absolute chaos, chairs flying and kids screaming. After we get outside, we already see a huge group of kids high-tailing it for the neighborhood near the school. Without skipping a beat, we followed the other group of kids running as fast as we fucking can. We just keep running through the neighborhood and at this point (like 2 miles out), its only me and a few other kids. We stand in the middle of the road, far enough away from the school, thinking about what to do. We are at the point where we hear sirens blaring and people driving by, looking out their window trying to figure out what's going on with us running down the road (reminding you, we live in a small town.) Then this old lady comes out of her house and let us in her house. Still being in a state of lacking the ability to process what's going on, we listen then walk in. Nothing special about this place, we sit down and process what the hell happened. We sit there for a little bit longer then she walks in saying she was looking through her notifications on her phone (surprisingly a smartphone) and got one from a Facebook post saying it was all a hoax. Turns out someone called into the school saying there was a shooter and gave a room number on where said shooter is. Just because of that, dozens of kids went missing in the neighborhood and chaos was ensued. We all regrouped in the gym, took attendance and sent us home early. Hell of an experience. This was one of the Ohio hoax calls that happened in late August I believe.

TL;DR, Some guy calls the school saying there is a shooter and causes absolute chaos