I recently served as a Juror...

I'm guessing they receive request like this a lot and need something to "prove" the information. Have you been to a doctor who knows about your condition - generally they will write something up on a prescription pad and sign it - they should not charge for it...

If that doesn't work and you can somehow make it to court the first day. In private during the selection process you can make this known to the court - generally you will be excused on the spot. They may ask stupid questions like " do you think this would affect your ability to render a fair and just verdict"

Hope one of these may work - second one sounds like it would be more of challenge...