That's the whole point of drafting -- to make it easy for the rider in back. Then, you're all rested up for your pull. Trust me, you get some big headwind you'll love taking it easy back there.

Once you're all rested and ready to pull, make sure you don't speed up but maintain the same pace as before (or slower if necessary) Remember, the poor person in front is looking for a rest now also. It's also OK to pull for a longer or shorter period of time, just remember that you don't want to blow up and not be able to sit on a wheel later (that's an ego move).