I'm Tired

I'm tired a LOT. As a matter of fact, I've written at least one journal entry titled, "Always Tired". But, today I'm tired because I had to get X-rays of my left knee which has been hurting for approx. a week. One "position" they wanted me in was agonizing and brought tears to my eyes. Another two or three were very painful. Why does pain and/or very high anxiety make someone tired? It could be (IMHO) due to our bodies trying to compensate for what it thinks is an attack that we are neither fighting against nor fleeing from. Or, perhaps it's because we are fighting our urge to flee. Either way, pain, anxiety and especially a combination of the two can make a person extremely tired!