It sure looks like the Navy has not changed much in dealing with medical conditions since I left the service all those decades ago. That is your immediate chain of command is composed of engineers who are only interested in the safe operation of the plant and watch station manning. Which of the two is more important to them is of question. I suggest that every effort to over look your medical condition will be made just so the watch rotation requirements can be met. When the time comes that your medical condition causes you to collapse or otherwise obviously perform below expectations, they will move fast to get rid of you.
There has been some good advice posted here about seeking all the medical work you can get while in the Navy and consulting JAG.
As far as medical treatment goes, sadly it is up to you to push the system for treatment or confirmation of the diagnosis or it's severity. As long as it remains boarderline, you will stay in the world of medical limbo. Keep in mind that boarderline means a decision on your future has not been made. Do not be intimidated by command structure or what rank or rate a person is wearing. You have a responsibility to your shipmates to be healthy enough to do what is expected of you, just as you have a responsibility to yourself for getting treatment.
You should to talk to a JAG attorney. The reason is simple. Whether the legal process to have you mustered out of the service has started or not, it is more then likely in your future. Given any discharge is a legal process, you need to know as much about that process as you can, and what options are available to you.
The point is, that once you are officially on the path to a medical discharge, your options for medical care diminish, as do your legal options. One of the things you need to consider is treatment after dishcharge. It is likely that your condition was not service related, but if service aggravated, VA benefits may be available. Again, your doctors and JAG can, or should help you here.
What has happened to you is unfortunate, but what happens in your future is up to you.