This is what happened a few hours back while I was installing a shelf in the bathroom.
The shelf requires three screws, but according to the stud finder, the screw locations I wanted didn't align with the studs. So I decided to use drywall anchors(a self-drilling type anchor about 1.5" long https://www.homedepot.com/p/E-Z-Ancor-Twist-N-Lock-75-lbs-Medium-Duty-Drywall-Anchors-50-Pack-25310/100040265) and pre-drill holes for the them. One of the hole locations was somewhat close to a gfci outlet, so I did AC scan using the stud finder and it didn't report anything.
So I went ahead and drilled a hole. However, when I manually screwed the anchor with a screw driver about one inch into the drywall, it felt like something was hit, so I took it out and pushed in my screw driver into the hole. To my horror, it hit something like rubber band inside wall, and I am pretty sure that it is a wire from that outlet, likely running horizontally since there was no stud.
I didn't notice anything abnormal – no sparks, no light out or flickering, no breaker tripping – and the outlet is working.
When drilling I believe I stopped as soon as the drill went through the drywall but the drill bit was likely pushed in a little further. Also, the tip of the anchor (plastic) is sharp. How likely is it that I damaged the wire? Should I worry and really open up the wall to check?
I think the chance is pretty slim, but I am being cautious and also a complete novice when it comes to diy and electric stuff, so will need some advice. Thanks in advance.