Disney's official answer to anything mobility related is,
Rent a wheelchair! Even if you don't need one or use one in everyday life.
Liability prevents CM's from assisting guests - even with a steadying arm! Some CM's may risk it but most won't.
And you would be horrified, offended, disgusted and shocked to see the extent to which cheating guests will try to exploit the system to "cut the line" or "get a freebie" or to be given a different experience. So no, they cannot take you at your word, your morphine pump, a doctor's note or anything else. Disney defaulted to the position of, "Rent a wheelchair if you have stamina or psychological issues." Sadly this is why you see so many more
ECVs and wheelchairs in the Park...
Can't walk more than a mile?
Rent a wheelchair! Have diabetes and get exhausted easily?
Rent a wheelchair! Have seizures if exposed to flashing lights?
Bring a blanket to cover your face and rent a wheelchair! Tripped, ripped a shoe off and have asphalt scrapes on your ankle?
Rent a wheelchair! Violently coated a trashcan in vomit?
Rent a wheelchair! I could keep going....
That's why the
DAS system had to change from its previous format. Now everyone is treated the same and those who have mobility issues are given extra time to join the line and
maybe not stand there for 45 minutes. But that depends on which ride we're talking! I think many people are waiting 4 hours for the Avatar rides...
And as PP pointed out, EVERYTHING about Disney is "waiting in a line" so if that doesn't work for you on vacation with such mobility issues, you may need to think about different destinations because the crowds are not going to improve in the next 5 years!
Everyone here has awesome advice and I think you should formulate a plan for your return trip to the Parks based on their information.