Funny I came across this. Took our first cruise in 2002, booked another Southern Carib in 2003. I was still swaying after 10 days. Would be in the supermarket and have to hold on. At work had to hold onto the walls every few seconds. Dr. treated me with a sinus infection that he said went dormant. I said I felt fine no suffiness just floor swaying. Not dizzy just swaying, I felt better as soon as I took antibiotic third one. I did have pressure problem on the flight ears kept blocking up and getting stuffed. I was taking sinatab on cruise so maybe something was starting. I am not thinking about it this time.
Ok, the part when the dizziness can make you fall over is not fun, nor is having a sinus infection. Both can be very serious. However, look at these episodes as an extra bonus to the trip. Just close your eyes when this "swooning occurs, and imagine yourself still out on thye deep blue sea. It's like a brief visit back to your cruise. The rocking should only last a few days once on shore. But, perhaps follow up with a physician if there is sinus pressure, infection or pain involved.
I know that getting and loosing your sea legs can be an experience. I do a fairly good amount of deep-sea fishing and it's funny how it can take a few hours to become steady on deck. Especially since we sometimes go out in very rough seas that toss our 90 footer around like a bobber. Then, it takes a few hours to get my 'land legs' back. The amount of time it takes to get them back is directly realted to how long you were at sea as well as how rough it was. If your body has to constantly adjust and steady you for a long period of time, you become more adjusted to that.
As far as your situation with this going on for several days, I think you may have an ear problem more than an adjustment problem. You mentioned some sinus discomfort and problems with your ears on your flight home. This sounds very familiar. I have had training in flight physiology ,and flying, especially with sinus problems(of any degree) can cause blockages that can cause the symptoms you describe. You may have blockages in the eustacian tubes that cause the inner ear to give you the unsteadiness and dizziness. Obviously, you doctor will be the one to diagnose this but I suspect this has nothing to do with the ship. If you doctor does not help you, check with an eye,ear,nose,and throat specialist and be sure to mention the problems flying.
I'm not a doctor but have a fairly large amount of experience with flight related problems and I have known many people with the symptoms you describe. Good luck