Trap Bar Deadlift "Cardio" Set

This was my final deadlift set for the day, after ramping up in weight and then doing two sets of ten with this weight (260#). I originally expected to get about 15 reps. When I hit that and still had some life in me, I decided to do 20. While I could have done at least a couple more reps, I never go to failure on deadlifts, so I was quite satisfied to stop at 20 before my form broke down too much. The rest of my workout consisted of supersets of bodyweight chinups and barbell overhead presses. For some reason I've felt fatigued the rest of the day.