Is it dangerous to do a skidding turn to lose altitude without increasing airspeed? I was taking some lessons in a light sport aircraft in South Africa a few years back, my instructor taught me something which I had never seen or heard of before or since. We went through an emergency scenario in which we had to make an emergency landing in a field (not really landing but just going through the motions, of course). I found a place to land and started my descent, but had to loop back around after I passed it. The instructor then told me to give full right rudder with left aileron to quickly descend without gaining airspeed. 

Wouldn't this qualify as a recipe for creating a spin and possibly killing myself? Should I actually implement that skidding turn in an emergency to land if need be?
As Ron Beyer pointed out in a comment, your instructor was showing you a forward slip - a pretty standard maneuver for light aircraft.

A spin would involve full rudder and a stalled wing, which usually means pulling the yoke or stick back a lot.  That's why overshooting the base-to-final turn can be dangerous - you likely already have a lot of rudder in and it's tempting to pull back on the yoke to try to tighten up the turn.  An unexpected spin at low altitude is not recommended as recovery tends to be both abrupt and fatal.

As long as you're keeping the yoke more or less centered forward and back and your airspeed up, there should be nothing to worry about.