An integral piece of the overall training picture is getting enough sleep. A sleepless night here and there is nothing to worry about, but if you consistently do not get the sleep you need and are training hard, your recovery from training will suffer. Circulating cortisol and C-reactive protein (a biomarker of inflammation) levels in the body increase dramatically in even short-term sleep deprivation.
In addition to the recovery benefits, research shows that adequate sleep improves motor skill performance (e.g. running) in adults. Takeaway: Make sure you sleep well most nights, and especially after a hard workout.