Having experienced a tail rotor failure in a rather large Wastelands product from a 40ft hover over the sea, I can assure you all that the previous theory lessons, good though they are, go straight out of the window!!.
In my case there was no warning, the helo just started to turn. Both myself and the other pilot automatically applied full opposite boot, thus we were both aware that tail rotor control had been lost before the end of the first 360 degrees. The rate of turn was rapid and disorienting but lowering the collective immediately significantly reduced the rate of turn - albeit in mid plummet.
We hit hard and bounced out of the sea into hover No2 where the a/c started to turn again before droppping into the 'oggin and rolling over. All escaped with no injuries.
Two lessons learnt from this. 1.In a hover you must lower the lever quickly, hack the engine if you can and cushion the touchdown with collective. 2.If you dont have your shoulder harness locked in every hover you are a prat!