I would have to say fatigue. I just got over being sick (or shall I say, I'm currently taking antibiotics and feeling much better, damn sinus infection), but being sick with a headache, stuffy AND runny nose at the same time, a sore throat, and an annoying cough kept me awake at night, leaving me totally fatigued. And that was by far the worst part--wanting to get up and move but just not having the energy to do so just sucks.