When you're at work and the power goes out, you can't leave, and....
Extreme temperature/humidity
The back up generators are on enough to still run the register/till/POS but not your work station (bonus if you lost all your work on a big order b/c it didn't save correctly)
Customers keep asking why the lights aren't on/when will they be on (bonus if this is happening in the middle of extreme heat or weather so the answer is obvious)