Negative g ???
Let's see, rotor blades detach, initial g around zero until vertical speed builds up towards terminal. So to get zero g requires no power at all.
Or to out it another way, with rotors suddenly producing no lift at all, g will initially be zero, no effort required.
In my personal experience rapid lowering of the lever at fast cruise can take the g a little below zero - things float up from their resting place in the cockpit - though certainly not as much as -1g. Not hard to see how, with the blades at flat pitch and airflow coming down from above due to the tilt-forward of the disc and attitude pitching down causing a negative angle of attack. What's not to understand?
Edited to say that if you have only flown helicopters that cruise around 100 kts or so, you probably don't notice it much, but at 150kts+ you certainly do.