The definition is disabled for the purposes of the 2010 Act is: -
‘a physical or mental impairment which has a substantial and long-term adverse effect on your ability to carry out normal day-to-day activities’
(I'm sure the above responders know that , as does the OP, I'm just setting a reference point).
The trouble with this is the weasel-words 'substantial' and 'long-term'. A fruitful source of inspiration for lawyers to argue all day long, no doubt.
There are a few conditions under the Act, where it seems one is 'covered' and automatically regarded as disabled under the Act - a medical diagnosis for cancer, multiple sclerosis or HIV. But so many conditions are progressive or fluctuating, and if you have one of these, than it is less clear cut. Do you have one of the 'I'm covered' conditions?
I'm wondering what happened on 26 March - did you finally receive a letter from your employer saying 'yes, we acknowledge you are defined as disabled under the Act' and also whether it said anything else?
There are then 8 days until 3rd April, when you presumably resigned, claiming constructive dismissal - hardly very long for even a recalcitrant employer who has had to be led by the nose to finally conceding your condition under the Act, to be telling you what adjustments it would be willing to make.
Not saying you are right or wrong, just considering the employer's potential wriggle room. They may claim you jumped ship from an unhappy employment, once you thought you were home and dry on an unfair dismissal claim.