How to make a workout even harder...

Get sick! I have been fighting a cold for a few days and woke up this am feeling much better.  I went to do my warm up and it felt like my legs were made of lead.  I could barely move, the cold has left my head it just hasn't vacated the rest of my body.  And the rest of the workout was way harder, it felt like the first time I went.  K did add extra weight to the last reps of everything...not helping.  To tired to even write much about the workout, as my arms feel like jello, and ache just typing, yes the workout was that bad. So loading up on protein shakes and hoping that will help my recovery!