Welcome to Healing Well! Soon we'll be welcoming you to our Wrapped Club!
If you haven't read my early recovery journal, it might help calm some of your fears. Here's the link: www.healingwell.com/community/default.aspx?f=45&m=2183443
I agree that two weeks is way too soon to go back to your full duties at work. I don't understand your surgeon's thinking. You will presumably have a hernia repair, as most people who need a Nissen have hiatus hernias. Most are told not to lift over 5 pounds for (is it? Correct me if I'm wrong. It's close, though.) at least 6 weeks.
On top of that, you'll still be recovering from the surgery, and you're not going to feel all that energetic.
Perhaps you need to go to your primary care physician and get permission to stay out longer. If you do go back, it should be on limited duty.
Don't worry. You'll do just fine!