I disagree with your approach. Just my opinion but I think you are giving way too much information in your letter. Have you considered just getting a note from your doctor?

I had to leave work exactly on time every day for a few weeks because I'm doing a procedure, TMS, that is every day. That means I couldn't stay for meetings or other after school day events. I ended up applying for a 504 with a doctor's note. I only gave them as much information as they needed to approve the 504.

I'm a little worried that you mention that some days you are suicidal. I would worry that your job might think you are a liability because of that.