Hello Minnah:
You legally do not need to tell anyone at work the details of your medical issues. You are protected under HIPPA and you do have the right to take FMLA. Of course your co-workers are going to know your gone, but they don't legally get to know why. Your HR department should be aware of that. (There are some requirements to qualify for FMLA, talk to your HR department or do a Google search).
I did not tell my co-workers. I went on vacation for two weeks and had the surgery. I had my bariatric doctor complete my FMLA form, so I could take time off work to go to my monthly doctor appointments. I requested that my doctor not use her stationary or any identifying stamps that stated bariatric on it. It is my right to protect my medical information.
My weight loss has been slow and gradual, which is why I chose this procedure. People are now commenting on how great I look. No one has asked what am I doing to lose the weight.
I thank them for the comments and tell them the truth. I work my butt off. I am now jogging on my treadmill for 60 minutes on an incline at least five times a week. I count calories, get plenty of rest, cut back on my portions and stopped the snacking.
I have had many surgeries and I have never felt compelled to discuss those procedures with my employer and co-workers. Personally, I believe keeping my personal matters and job matters separate. When I go to work, I don't talk about my personal life and when I go home I don't talk about my work life.
Anyway, just my thoughts on the matter.
Best of luck to you!