(Edited to reflect light disk loading helicopters)
The state where the rotor is in VRS is strictly defined by the ratio of the descent rate to the downwash velocity of the specific helicopter. Only within that boundary is VRS possible. One caviat is that we read RoD with a static instrument, which can go flakey when the wash around the fuselage is skewed beyond the normal certification envelope.
For modern helicopters, VRS is unlikely below vertical speed ratios of .5 and beyond ratios of 1.5. For an R-22. descent rates less than about 700 fpm are below the VRS threshold, and descent rates beyond 2100 fpm are above VRS. For Black Hawk, descent rates of about 1200 FPM are below VRS and greater than 4000 FPM are above VRS. The Vortex in VRS is produced when the downward velocity matches the rotor's downwash, so the exact match causes the air to simply wrap around the rotor tips. Lift is lost quickly, and the bottom falls out. If the power is left up and the condition is stable, the descent rate is constant and very high (about equal to the downwash velocity - maybe 1400 fpm (robbie) to 3000 fpm (Hawk)). The thrust variations might be 20 or 30% thrust (producing low frequency turbulence that is about .3 G's).
If you lower the collective in VRS (and you have lots and lots of altitude) you will simply get into windmill brake state and autorotate at about 5 to 6000 feet per min.
For data and photos, see my web site at:
http://mywebpages.comcast.net/llappos/
During VRS, typical modern helicopters retain some cyclic control. The rate of descent will make the horizontal tail try to pitch the nose down, which will help you recover. Reduced collective and nose down will produce a fast exit from VRS. Increased collective will only help if the aircraft has a great deal of excess power, not at all likely in anything but an empty machine with powerful turbine engines.
Note from the data on the web site that VRS is unlikely in a purely vertical descent, some forward speed is needed, maybe 8 knots. In practice, it is difficult to attain and hold VRS, as the condition is unsteady and tends to break of its own if any disturbence is induced. That does not mean it can't do harm, since the first 1000 feet of drop might be several hundred feet too many!