I did a detox apple cider bath , one hour later i was very tired had a headach , the next day my left side hurts and my back why ?

I can't explain it: I'm not sure the apple cider had anything to do with it, unless you added something to the bath. If it was very warm/hot, your blood vessels could have dilated making you feel "washed out" or tired. Vasodilation could have contributed to headache as well. My only thought about your left side/back is that you were cramped in the tub. Hopefully all is improving! Doubt any serious harm. Good wishes