Welcome back, Marilyn!
Disney Cruise Line has a physician and a nurse on call each day on the ship, 24 hours a day, so there will always be access for guests to medical help should it be required. You can read a bit more about the
medical information including doctors onboard on Disney Cruise Line's website.
If you think you might suffer from seasickness, it's usually recommended that you take medication before you get onboard the ship as well as during your cruise. The medication is more preventative, as I understand it, than a remedy once you are already feeling sick. If you do find that you feel seasick, go out on deck, look out at the horizon, then close your eyes and take some deep breaths. When you open your eyes again, look back at the horizon. This is said to realign your inner ear and help with the nausea.
I personally do not suffer from seasickness, but I know many who have sailed with us that have, or didn't realize it until they were onboard. If you don't bring your own patch or other medication from home, there are seasickness medications, patches and wristbands for sale onboard, so don't hesitate to stop down to purchase one if need be.
Stop back with any further questions you might have, Marilyn!