Hello Jeff
That's just too bad. You've been waiting for this job and get struck down with a flare before you've had a chance to get stuck into it and prove yourself.
I don't know what government jobs are like in the US, but in the UK they really look after you. I know you are on a trial period but I think like Donette said, if you chat to HR about it, I would like to think they would do everything they can to help you.
Like you said, it's not as if you can hide your condition at the moment, things are too bad. I think putting yourself on their mercy is your best chance at getting support and understanding.
You don't want them to misinterpret the situation as you are not pulling your weight for example.
I don't know what work you do, but when I was in a bad way at work, my boss let me work from home for a while. Of course that certainly may not be an option and you also mentioned travel. When I came back to work I was put me on light duties too.
I hope your boss and co-workers are kind and supportive, Jeff, you really deserve a break here.
Good luck and very best get well wishes.