The symptoms are yawning, a nodding head, dreaminess, and a slight reduction in energy. To a cyclist, this is the least important cause of fatigue, but it can still reduce speed by a mile or two per hour. The only cure is a nap, although people sometimes use drugs to keep alert longer. Several cyclists reported nearly falling asleep or hallucinating. Also, if there is no real cause for being drowsy or the problem is persistent, see a sleep disorder specialist.
Skin burn is caused by too much sun and occasionally by too much wind.
The symptoms are red or redden skin that's hot to the touch, a washed out feeling, and mild dizziness. Wind burn only produces mild effects, but sunburn can be life-threatening and is a leading cause of cancer. Even the mild forms are much worst than missing a few hours sleep. The only cure for skin burn is slow healing, although skin creams can help. Heart fatigue is caused by pushing too hard for your fitness level.