When I was in the U.S. Navy aboard a 760-foot heavy cruiser, there were times when nearly everyone onboard was seasick. This was the case in the North Atlantic during Hurricane Hazel. At times there were a couple dozen guys in sick-bay, strapped into their bunks with a trashcan tied to the stanchion to prevent it from moving away. Several had IVs in their arm to keep them hydrated. We didn't have anyone die, but we did have a couple sailors airlifted to a base hospital to recover, which sometimes took a week or more.
As for rupturing anything, it's pretty much impossible. Granted, if you have the dry heaves, it may feel like something is going to burst, but this is the result of esophageal spasms, which causes the person to wretch his or her guts out, while producing little or no stomach contents.
Dehydration is the main concern with seasickness. The best way of avoiding this is to keep yourself hydrated at all times. However, instead of gulping down a bottle of water, just take a few sips every five minutes or so, thus allowing the fluid, preferably water, to be metabolized into the system and not lay in the stomach. Ginger-ale and Coca-cola can provide you with other needed nutrients in the form of carbohydrates from the sugar content, plus has the added benefit of a soothing effect on the stomach. However, the carbonation adds gas to the stomach, which is not what you want to do to a person experiencing motion sickness. It's best to allow the soda to sit in an open container until most of the carbonation evaporates, and drink the contents ice-cold and flat. Far fewer problems, but not quite as tasty.
The vast majority of seasickness remedies are nothing more than potent antihistamines, and they usually work best when taken before motion sickness symptoms begin. Side effects, and they all have them, usually consist of dry mouth and drowsiness, but in some instances, the effects can be more severe. In rare instances, the side effects can be fatal, therefore it's best to consult a physician before taking any medication that you don't normally use.
I've been very fortunate in that I have never been seasick since I got out of the Navy. For some, unexplained reason, while aboard that massive ship, I heaved my guts out for several days, sometimes up to a week, before I got accustomed to the slow, rolling motion. Put me on a smaller boat and I'm fine. The one caveat to that is I cannot stand the smell of diesel. That seems to set things in motion and really makes me feel rotten while at sea. I don't think I'm alone with the diesel fume reaction, because everyone else I know has the same problem with diesel fumes.