Starting a new chapter

My surgery date for the Rouen-Y Bypass is next Friday! Jan. 17th. It will be done in Cleveland Clinic by Dr. Aminian. I am 65 and this starts a new chapter in life. I've lost 34# to reach my goal weight. I'm so excited. However, having some trouble. I am one week into my protein shakes (800 cal) and clear liquids. I am so weak and shaky. Does anyone know if this just me having to adjust and it taking time? I'm afraid if I am feeling this way after surgery, I will fail. This is not a good feeling! I wont be able to exercise. What's your thoughts?