After having a shut down and some med-related issues, I asked for some 'accommodations' by way of a letter from a psychiatrist.
Basically, I asked to be moved to a desk with less fluorescent lighting, which my work was happy to do - my desk now faces the window so I only have natural light directly in front of me. The alternative was that the light be changed to a warmer tinted light.
I did ask for other things, like to be removed from the telephone pick up group, but this hasn't happened yet (it's been 4 months so I'd say it's been forgotten about), and to be given more space, which has kind of happened incidentally. I've also been told I can wear my headphones if I want, but this was already acceptable prior to the discussions about accommodations. It's just not a realistic thing considering I work in a role where I have colleagues, managers and such approaching me on a regular basis and now with me facing away from people, I tend to jump/get startled if someone approaches me from behind without warning. So I don't wear my headphones too much now so I can hear people approaching.
Like you, Kraftie, I guess the best accommodation I have to date is people 'tolerating' me. I am very open when it comes to the fact I am different and I think it helps to be able to have a laugh at your own expense sometimes...helps people tolerate I think.
EDIT: Oh and I got a formal accommodation to be warned of fire drills before they happen so I can remove myself from the building prior to all the hoohah. The sirens, the people, the stairs, the break in routine, it's a sensory nightmare for me.
So TL;DR: formal but informal.