Welcome to the Healing Well Wrapped Club! What you're describing is perfectly normal. The first week constipation is probably a combination of not eating and drinking much in combination with the narcotic pain meds which are notorious creating problems.
The second week with diarrhea is likely a reaction to the assault on your upper GI tract. Your stomach has undergone a big revision, and it's showing its displeasure with diarrhea.
I used to tell my doctor that I had a "potpourri of poo"...it would change from day to day, week to week. It was just my GI tract trying to accustom itself to the creation of a new LES backup system!
You can also experience "dumping" at this point in your recovery. It's a premature emptying of your stomach contents into your intestines, and it creates diarrhea as well. You can sometimes know when it's happening because you'll hear lots of gurgles.
Here's a URL for a good document regarding what to eat post Nissen. Unfortunately, no matter what I do, I can't get it to be a live link, so you'll have to copy and paste it into your web browser.
Also, here's a link to my early recovery thread here on the forum. It documents my first 19 days post op. It might help you with knowing what's in the realm of normal during recovery. While everyone's healing is unique, there are certain things that we all experience.
Unfortunately, surgeons (pretty much universally)don't prepare their patients for what they will experience during recovery. I don't know why...
Don't worry...the first couple of weeks are the worst. Healing is gradual, so don't expect to see a sudden improvement. Also, remember that your insides have undergone major surgery, even though you wouldn't know by looking at those 5 little incisions. Your outsides will heal quickly, but it'll take six months to a year for the insides to heal completely. That said, you'll find significant improvement long before six months, so don't panic.
I assume your surgeon didn't tell you that your wrap will become increasingly more swollen during the first two weeks, to peak at on or about 14 days. Don't be surprised if your swallowing gets worse before it gets better.
If you can surrender to your recovery and follow it where it leads, you'll find it much easier. Those who struggle against it have a much more difficult time of it.
I'm glad you've joined us. People here have been through what you're experiencing. You've posted in the perfect place...right on the main page. I'm sure others will be by to welcome you and offer their support. Keep asking questions! We'll do our best to answer them.
Hang in there...it'll get better!