To get long term sick benefits you need a strong diagnosis made by a physician and you have to prove that you are unable to work because of disability from your disease.
The diagnosis is in the hands of your doctor or the specialist he has or is going to refer you to. The only need is a written diagnosis that has to be written on a special form that your doctor has or is going to get once you have applied for benefits. Your doctor will help you with that.
Then you have to prove that you are disabled and cannot work. I don't know if in Ireland there are specific tests that are applicable for that. Many tests do exist and there are variations from one country to another. Many countries do not have specific tests and this is up to your doctor or specialist to find out. For example there is one on the following site that you may try http://www.magnetic-field-natural-cures.com/XX.html but remember that it may not be the one to be used in your country. I did ask a few doctors with medical expertise in courts. Some of them, out of pure interest, have tried different tests on the same person to find out that the end result is always the same! The test I have indicated above is quite good as it explores your limitations for a range of everyday life activities that makes easier to appreciate your disability for work. Make a memo on which work you had before and explain why you would not be able to do it because of your condition. Also, if you have been proposed work adaptations or you have tried other work, write down why your disability did not allow you to carry on. Once you have gone through those 2 steps, you may be referred to another doctor who will decide about your status. I have heard that in UK sometimes this interview is done over the phone and sometimes you have to be examined.
In any case, if you have done the free test for fibromyalgia on our site at http://www.fibromyalgia-information-relief.com/fibromyalgia-test.html it is worth taking the pain drawing with you so you can show the pain and the test results so you don't forget in case you are tired and get foggy brain on that important day!
Also make a list of all your medications that you are taking and the ones you have taken in the past (and their side effects or failure) as well as a list of all doctors you have seen.
If you are denied benefits, you may appeal. Don't get discouraged, it may take long before you get results.