according to my medical education, I can tell you that anxiety is a very broad term and you can't explain it by a single word.
what I think about anxiety is what you experience during exam days. psychologically, you have some sleep disturbances, restessness and concentration problems. your body also responses to anxiety through sweating, shortness of breath and in serious occasions palpitation and shivering.
I agree you that all these reposes from your body is that it tries to defend yourself from emotional threats