Hi there, I wouldn’t worry about this - the purpose is to assist you.
“Reasonable adjustments” do not have to mean reduced hours - although that could be one of the options discussed - but you cannot be forced to accept reduced hours (and pay) if you didn’t agree to it.
They will be looking at any practical measures that might help. Do you need a disabled parking space, for example - assuming you return to driving? Are there any aspects of your job that are causing a particular problem, that could perhaps be done a different way, or is there some kind of tool that might help? Is your office (or wherever) furniture and equipment OK? Or do they make things unnecessarily difficult? Could you have different?
Would flexible hours (not necessarily reduced) be possible, or help? Is there any possibility of working from home sometimes?
I don’t think you need a confirmed diagnosis to discuss these sorts things. Simply consider how you are affected - and what, if anything, might help. Does the workplace get too hot for you? (Many people find symptoms worse with heat). Do you need a fan? Sometimes it could be very simple and minor things - not major changes to terms and conditions.
When I was still working, a small concession I had was that I was NOT expected to carry my laptop everywhere to meetings, especially as I don’t drive, and would occasionally have to visit a customer miles away on public transport.
Ordinarily, employees were supposed to take their laptops with them everywhere, but I got an agreement that was not expected, and turning up with a notebook (not the computer kind) and pen would be OK. If a laptop was essential, they’d find a loan one for me at the destination. I also had things like I MUST have prebooked seats on trains, if I was visiting a remote site, as I couldn’t risk having to stand all the way home from Reading to Bristol (as had sometimes happened).
This meant meetings I was in couldn’t overrun, so that I would miss my train - or if they did, I would have to be excused without anyone holding it against me. If necessary, the customer would have to be told I had a health issue that affected my ability to travel, and that I couldn’t be left to struggle all the way home, in rush hour, without a seat!
All pretty commonsense stuff, really. Not lugging more stuff than necessary, not chancing travelling without a seat.