With the helicopter in forward flight, the cyclic is used to hold the disc in such a position that the desired airspeed is maintained. This position is an equilibrium position into which the disc has settled, after the effect of flapback has been allowed for with forward cyclic in setting the desired speed.
If the lever is then raised, there is an overall increase in lift across the disc, and the disc will rise to a higher point in the direction of travel i.e. the nose will rise. If airspeed is to be maintained, then further forward cyclic will be required to overcome the new level of flapback.
Conversely, if the lever is lowered, there is an overall reduction in lift, and the disc will move to a lower position in the direction of travel i.e the nose will drop. The cyclic is still at its original position, and is now too far forward for this reduced level of flapback, and must be moved rearward to maintain the original airspeed.