Insomnia is the inability to fall asleep or the inability to stay asleep. Sleep apnea is a breathing condition which causes the sufferer to stop breathing, then wake up gasping for air in a cyclical pattern. Both insomnia and sleep apnea prevent you from getting a full night of restful sleep. Chronic lack of sleep leads to fatigue, irritability, restlessness and can also eventually weaken your immune system. Lack of sleep also causes clenching of the teeth at night, which puts pressure on the TMJ causing multiple TMD symptoms. Without proper sleep, you lose your ability to be alert, productive, and energetic during the day.