The very best Applicant's Statements, meaning the ones that really help win a case, come from clients who kept a journal of their experiences with their medical condition. They are able to tell a story about the pain and suffering they went through, whether physical or psychological. Their stories make it clear why they couldn't perform parts of their jobs and connect the dots between their medical condition and not being able to work properly. The more of a story you can tell on your Applicant's Statement, the more it will convince the adjudicator that you are genuinely disabled. The most convincing facts are the specific things that happen to you. That's why dates are good. You are, as we say in law, corroborating your own medical condition with contemporaneous notes. It is a time-honored way to win.
To be more specific, your aim in keeping this daily journal is to focus on the particular issues OPM asks in it's Applicants Statement.
Here are those specific questions:
4. Fully describe your disease(s) or injury(ies.) We consider only the diseases and/or injuries you discuss in this application.
5. Describe how your disease(s) or injury(ies) interferes with performance of your duties, your attendance, or your conduct.
6. Describe any other restrictions of your activities imposed by your disease or injury.
To repeat, if you keep a contemporaneous, written journal of your plight related to the above you will be able to use that when you answer the above questions. You will be able to spin out a real story that will give the adjudicator a feeling for what is going on. You will have a convincing story of illness and/or inability to come to work that will be a powerful way to sell your case to the adjudicator.
Bottom line, you don't want stilted language when you tell your story in the Applicant's Statement. You want your human condition to shine through so the adjudicator can understand your pain and medical condition as it's connected to your official job description.