We just got back from a trip to Coco Cay and Nassau (Apr 13-18; Sovereign of the Seas). The water temp at Coco Cay was a little cooler than I remember around the same time last year when I was at Daytona Beach. Of course, it was also much warmer outside last year (high 80's) versus when we were at Coco Cay (high 70's). However, the day we went to Nassau, the outside temp was warmer (mid 80's) and the water felt warmer as well (we went to Paradise Island and played in the water for a long time). Nonetheless, I acclimated to the water temp pretty quickly. I'm from Oregon, so any ocean water temperature over 50 degrees feels warm! If you go snorkeling at Coco Cay, I would suggest doing it when the tide is in. We got there on one of the first tenders and were glad that we did. We saw all kinds of fish, even a small shark! Not sure about the jellyfish; I didn't see any where we were (but we really didn't do much snorkeling. Mostly, we just laid on our beach mats in the water). My wife and I both loved Coco Cay....we didn't want to leave!! Have a great time!
We were able to easily get on the first tender. Most people arrived at the island around 10 (we got there at 8:30, I believe). I don't know if that's common, but I wouldn't be surprised if it was (people arriving late AM). Another thing I'm not sure about is how many people are required to be on a tender before it departs for the island (I never asked if they left every 30 minutes, or just when enough people got on)?? There were already folks on it when we got on and the boat left soon after...of course, they must have been waiting just for us If you have any other questions, I'll try to answer. Hopefully, someone with more knowledge about this will pipe in.
PS--feel free to email my wife and I if you have any other questions about RCL or the ports. Our email is firstname.lastname@example.org.
Sorry you're not feeling well You should definitely talk to your doctor to see if he/she thinks it's okay for you to go. If you have cruise insurance, it should cover illnesses that are not chronic. If your doc gives you the thumbs up, then I believe if the medicine bottle is labeled (indicates the doctor's name, phone number, prescription type/count/dispense info), then you're good to go. I brought some pain medication that I take on occasion for my back, and it was never an issue.