NO such thing as can't daisygirl. I did a forty day Water Fast (losing 57 lbs) whilst working full time and training two racehorses. Day 35, 36 and 37 included riding work on the gallops in the snow.
Days 1-10 are hard, you miss eating but the huge weight loss is an encouragement.
Days 10-30 are bliss - hardly even think about eating, something you just don't do at the moment.
Days 30-40 are (or were for me) hard, but having got this far you can't give up.