A long time ago in a high-energy lab far, far away...
We were testing a transmitter for a phased-array military radar. These devices were pretty heavy duty as the peak power output ran into the MW range and the power supplies were just as beefy.
Because of the lethal potential (ha ha) of a lot of the equipment inside the room (about 30m x 20m x 10m, fully shielded), one of the rules was you didn't ever work on something on your own. I remember a pair of us coming in one afternoon and hearing this muffled rhythmical thumping from the other side of the room; on closer inspection we saw a twitching pair of legs sticking out from under the transmitter.
We immediately hit all the emergency cutoffs, then went in with the earthing sticks...
It turned out that one of our more senior engineers (who should have known better) had decided to do a bit of work on this device. After he came back from hospital, badly bruised but without long-term injury, he explained that he'd brushed a high voltage terminal whilst working under the radar and that had flung him away. Unfortunately, he bounced off the floor and straight back into the wiring, which threw him back at the floor etc. Very luckily for him we had chosen to walk into the lab, pretty much at the same time as this started - I've no doubt he would have been killed within minutes without intervention.
KIDS! DON'T DO THIS AT HOME!