Painful Treadmill Work

I probably should have done this set in the morning, but thanks to a very supportive person, I managed to accomplish the task this evening.  The set was 4x 5t, 2r with warm up and cool down.  I set the treadmill at 5.5mph for recovery and 7.5mph for tempo (10:50min/mi, 8min/mi respectively).  The first set was hard, but not impossible, the second set was painful.  By the third set, I was purely willing myself to continue and I really didn't even want to start the 4th set.  By the time I got there I was having trouble keeping up with my pace, so I did the first 2 minutes at 8:00, the next minute at 8:06 and the last 2 minutes at 8:13.  Nice, solid plateaus.  I did what I was supposed to.