You know what's worse, ever played at a club and you approach the mic to sing that first note...your lip touches the microphone and BAM ! You feel like you lost a tooth filling

One local club I played in often, had a grounding issue onstage.
There was a guitarist on one side of the stage, and me (with a guitar) on the other, apparently plugged into separate circuits. Neither of us had electrical issues on our own, but if we touched we got a huge shock.  We used to chase each other around the stage, or try to sneak up on the other to zap.
The good old days... lol

 
I have this installed on my main power bar for live gigs.. There's been a few times it showed faulty wiring. Just last year at an outside event it showed the Hot/Neu reversed.  I followed the extension chord to a supply box someone had jerry rigged and the outlet we where given was the problem. The other outlets were fine so I swapped it over leaving some food vendors to fend for them selves. It rained a few times that day to boot. 

I've had this and it can really throw you off during a jam

I had similar recently at a gig where my guitar was giving me an unpleasant tingle and the metal power switch on my Vox amp was doing the same. It turned out to be caused by an extension cable real still having most of the cable on the real. It was causing some kind of induction. I unwound the cable it all was well. So it's not always an earth problem and this is one to watch out for!

Coiled extension leads indeed act as inductors. Among other problems arising from that is that they behave like the element in an electric heater and get much hotter per amp of current than when unwound. It's not unknown for the insulation to melt or voltage to break through the insulation if the current's too high - they're a fire hazard as well as the risk of shock.

A lead that's rated at 13A uncoiled might be only safe for 6A (sometimes less) when coiled on its spool.

Hi...i am a new user here. It sounds like you may have an issue with grounding or possibly the hot and neutral have been reversed. This puts voltage on things that are usually grounded. In Canada or the USA, if you have an old amp with a 2 prong cord and plug it in, there's a 50% chance that power has been connected to the chassis and into the guitar via the ground circuit through the guitar cord.