Hi, first wishing you the best on your new journey. The best would be to discuss your fears with your doctor, prepare a list and make sure you get answers for each one of them it might put your mind at ease.
As far as discussing your procedure with your coworkers you dont have to. Many people that want to lose weight need some type ofhelp to achieve their goal, a trainer, a doctor, a nutritionist and your surgery is one of those tool. You certainly have no reason to feel ashame for improving your health on the contrary you are brave to do so.
When the pounds will start falling off and your coworkers start noticing and commenting just smile and say thanks and if they ask how you are doing it, just say that you decided to change your eating habits and that you are very serious about loosing weight.