When I first started diving, I experienced quite a bit of motion sickness. It would never be a problem before a dive, but it would be a real problem upon surfacing. I would feel nauseaus at the surface and on the boat, and the feeling would slowly fade once back on land.
I learned a few tricks to minimize motion sickness. Medication probably helped the most, but I also ate better and drank more water. I also chugged a special soda immediately before diving; the soda contains an acid that counters motion sickness.
Over time, I noticed that my motion sickness decreased. I would dive unprepared, which is to say I hadn’t taken the medication or drank the soda, but I would feel relatively well after the dive.
I still take all precautions before a dive, just in case. However, it seems that the body adapts and naturally becomes less susceptible to motion sickness over time.