1. The boat rocked so much that I got sick.
2. The boat rocked so much that I got seasick.
(Does #1 mean #2?)
Yes, they mean about the same thing.
#1 would apply on any body of water (lake, river, sea, ocean...), while #2 seems to apply mostly to being out on the ocean or a very large body of water, such as the Gulf of Mexico or something like that.