Originally Posted by slownsteady
You mentioned that you get a little shock every once in a while from the existing switch. That is probably bad news and you should look into that before anything else.
Originally Posted by zannej
when my regular bathroom wall switch gave me a slight zap when I flipped the switch with damp hands.
There's a slight potential difference between the switch and whatever else conductive surfaces your body parts were touching at the time.
Assuming ~1 mA of current flowed through your ~1 kohm wet-skin+body+wet-skin resistance, this potential difference might be 1vac or more.
The first step is to measure the voltage between these two points. The next step, how much current & power this voltage can possibly deliver, is slightly more complex.
It may not be fatal but you ought to trace this down. If you can rent this
you'll be way ahead of almost everyone as to being informed about your house wiring.
BTW, bathroom lighting can be tricky in order to avoid unflattering lighting angles. Lighting from the sides seems to be OK in all cases.