i would evaluate the way i feel and base my decision on that.nevertheless,due to my busy schedule,i got into the habit of sleeping 4.5 hrs every night and got great results doing so...but after 8 months on this schedule,my body gave out and forced me to take some time off.now,i attempt to sleep 7-8 hrs/night even if it means sleeping @ 8:30pm in the evening and my results have improved tremendously.in my opinion,take a day off and recuperate properly and then proceed w/ your training the following day!!!fyi