I got seasick twice in my 9 years military.
Heavy weather only bothered me (as in seasickness) one time.
100' tug used to bring Lexington into berth at P-Cola.
We were due to go into drydock over in Mobile Al for bottom work, pumped off all SW ballast, the lead shot, and FW, and left just enough fuel in the diesel tanks to get from Pensacola to Mobile. Dang old tub was built in 1945, and this happened in '76 so she wasn't the most modern vessel in haze gray paint to begin with, but with no ballast it lost lots of stability. We had a flank speed of about 6 knots in good weather--you can drive to Mobile from port in 45 minutes. Took us 3 hrs to make the trip. We hit a squall right after we cleared seabouy and rocked & rolled all the way to mobile like a little bobber. I stayed in the engine room for the first couple of hours till the bilges got stirred up good and the smell and motion drove me topside. The steel picnic table that was on the fantail was gone, so was the p250 firepump that broke loose, and the galley that was going to fry fish for our lunch looked like a disaster area. The whole crew except the old crooked finger masterchief craftmaster was plopped down by the fresh air intake vent, when they weren't upchucking over the side. I didn't loose my breakfast but I sure wanted to. There was a payphone at the dock in Mobile, and I seriously considered calling my wife to drive over and pick me up, but we hitched a ride on another tug going back and the gulf was smooth as glass that afternoon.
The other instance was airsickness. Before being approved to fly as door gunner, you had to show your ability to hit a target from a moving helicopter. All us new gunners went up one morning, out in S. China sea just southeast of Danang, threw some wooden pallets over the ramp with dye marker nailed to them for targets. Pilots flew figure 8s, which allowed both left and right side gunners to acquire the targets, and as you know, for any aircraft to make a turn, it has to yaw over a few degrees--the tighter the turn, the more degrees you yaw over, and we were making tight figure 8s to keep the pallets within accurate range and in visible sight.
Watching that horizon move 40 or so degrees with each each turn wasn't a happy feeling, and we did it for hours, till we all got a turn, then we did it some more as the pilots went thru every possible simulation of what we might encounter entering or leaving a hot LZ. Then too, I didn't actually upchuck, but if we'd stayed out there much longer I might have. Some of them did--crewchief opened the hellhole so they wouldn't make a mess in his helo.