Worried about being sea sick. 
Been on a few cruises, both large ships (Oasis) and smaller ones (Amsterdam).
Don't worry about seasickness. Get a cabin near the middle of the ship and not on the highest deck and you will hardly notice any motion in anything except the heaviest of seas.
Take along some anti-nausea meds (Gravol) and don't be afraid to take them if things seem like they may get rough. Candied Ginger also works wonders with nausea. I was worried about the sugar on the Ginger, but realized we were eating and drinking like pigs so......
Go for it, cruising is a different way to vacation.
It isn't for everyone, but it hooked me, and I had to be dragged kicking and screaming by my wife. I'm glad she persevered.
