I won the Tour of Park City on two hours sleep but failed average workouts after a good night sleep 
One or two nights It might be worth rolling the dice to see if you can complete them unless you wake up feeling absolutely awful obviously. That being said, if a lack of sleep becomes an issue for more than a couple nights it might be wise to do the famous listen to your body thing, and get a little extra rest before you start pushing it. Pushing it while tired as a great way to get sick.
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