Jury duty is usually for your county, so it is separate from most federal and state gov.
I don't know if your county has a website that has more details about jury duty?

If you have your accepted disability papers that might be all you need for proof to be excluded from jury duty. Or I think a official note from one of your drs would suffice as well.

this is what my county website ( Oregon ) says
[For other types of excuse requests, you must show good cause why you should be excused. Requests by phone to be excused by these standards are not accepted. If you are self-employed or not paid by your employer for time spent on jury duty, you are not exempt from jury duty. If you have a critical medical condition, or otherwise have a critical conflict with jury duty, you must explain your situation in writing. Include proof such as a doctor's complete explanation, including whether or not you work outside the home, travel itinerary or copy of tickets, etc. In most cases you will not be excused, but we may be able to defer your term of service to a date not more than one year from your original summons. In your correspondence, propose several dates which you can serve (No Mondays)….Send your letter immediately. The court will act promptly on your request. You will be notified if your request is denied. Send letters to:]
and
[Anyone with a disability who needs accommodation to participate in jury service may advise the court of the disability and type of accommodation by telephone, TTY, or letter as soon as possible prior to jury service. ]
http://courts.oregon.gov/Washington/...faq.aspx#jury7