As long as you get any boat rocking sensation,you acquire sea-legs
(or seasickness-take your pick) doesn't matter how small the boat is
(actually the bigger the boat, the less motion) or on a lake or river or the ocean (ponds have the least).
Pontoons are quite stable, but they still have motion of pitch & yawl
and still rock in the wakes of other boats, too.
It still can take a while before you get your land-legs back. The longer you are on the boat, the more time it takes. We used to go out for a week or 10 days (our 25' sloop had a head, & galley- and slept 4 or 5, nicely).and only got to shore every 3rd or 4th day. Maybe twice or 3 times during the whole vacation. We would 'gunkhole' on the Chesapeake Bay and sleep and cook on board. I'd be 'rocking' on land for an hour or more when I went ashore.