It depends on your technique. If you have the technique down it isn't difficult to rapidly decelerate on hills. It's mainly just a matter of bracing yourself, keeping your centre of gravity back and modulating the brake.
If you're not prepared for it and slam the front brake on your weight will shift forwards and you'll have lift off.
Riding trails for so long I sometimes take for granted the instinctual awareness of center of gravity without which its impossible to become even an intermediate mountain biker. Getting your weight back makes all the difference going down hill.
The bigger problem on a road bike are the skinny tires and twitchy handling make it very easy to fishtail and topple over when braking at speed.
If you're not prepared for it and slam the front brake on your weight will shift forwards and you'll have lift off.