My head shakes back and forth as though I'm saying "no" except really fast. Only when I get nervous or uncomfortable.?

Essential tremor. Is when you have uncontrolled tremor in parts of your body. It is known to be familial condition, meaning that it runs in your family. Because there is no cure for the condition the treatment reduces the severity of the tremor. Rec.: see a neurologist for evaluation and management. Good luck.