Lisa, I am not affected by the condition. I am very familliar with it, only through clients who have booked cruises. I am an agent for one of those online mega-booking agencies. I have had a number of clients with the same condition. The process is different with each cruiseline but Carnival has a very good program for special needs of all kinds. I'm assuming since you aparently booked direct they have sent you the special needs form. Fill it out in detail. They go to special lengths to assure you won't have any problems with your dietary needs or cross contamination.
I don't know if there are some on this forum with the same condition, I doubt it, it's relatively rare. I can only speak from second hand information but I've never had a single issue with Carnival or any other line with the dietary requests. There are many many issues they have to deal with on a very regular basis. Seafood and peanut alergies, some life threatening in severity. Many don't realize that with a peanut alergy, just foods cooked in peanut oil can be fatal. Same with Celiac Desease if it's severe and the wrong bread is served. I can't say issues have never happened with the cruiselines and such special needs but I've had very good results with their Special Needs Dept handling each issue seriously and the ship staff also taking the preparation and serving seriously.