In both powered flight and autorotation, unloading the disc, ie moving the cyclic forward, causes the rotor RPM to decrease initially. It will then increase as you pick up speed. If you then flare, you'll get an initial increase in RPM, then a decrease as you slow down. In powered flight the governor usually masks the rotor RPM changes. The reasons have been explained as clearly as I probably could, though I'm sure someone else can add more detail if you want it.