You may qualify for a
DAS. To me it sounds like you do have symptoms that might qualify. No one here can definitely say yes or know, but I think it's worth asking. Just remember you have to be able to explain your needs that do not relate to mobility or stamina. WDW would see balance as part of the mobility or stamina issues.
A mobility aid (including cane or walker) indicates to CMs that you will need an accessible entrance. For most attractions, that's the regular standby line.
Also, one thing to think about when it comes to thinking about mobility aids is that overdoing it because you wanted to be "normal" at Disney could actually lead to overall regression. Is it really worth walking/standing at one of the most wheelchair accessible places in the world when it could result in longer-term problems (which could include going "backwards" to using a wheelchair)? I've, unfortunately, learned this particular lesson the hard way and not even for something as fun as a WDW trip.
There's also nothing that says you have to use a wheelchair or
ECV all the time. Plenty of people use them between areas and in the longer queues, but walk through shorter queues and shops/restaurants/etc. So even if you choose not to bring a wheelchair or ECV, I'd bring the contact info for one of the off-site vendors. Personally, I'd go for the ECV, if you do choose the seated mobility aid route, because it'll give you more freedom to get around and it's easier to carry canes with you if you need them when you walk. Of course, at WDW, the only people you're likely to see who are from your life at home are the people with you, in case that factors in.
I'm coming from the opposite perspective in that I wasn't particularly mobility-impaired until I was in high school. The condition I have is variable and gradual. I can walk short distances using a walker (or furniture "surfing"), but use a wheelchair (both manual and power) for longer distances. I have a more "normal" life with a wheelchair than I ever would if I tried to fight to get around with just the walker. I've actually been using a wheelchair for longer distances since I was just walking with a cane. I've also watched friends with conditions like CP who at one point "progressed" past needing a wheelchair (some even got to the point of walking fully un-aided) and have, as an adult, started using a wheelchair for some things because it means they can do more/participate more in the world. It doesn't mean that they've "regressed", and often actually leads to their being able to be more "normal". There's nothing lesser about you if what you need is a wheelchair, ECV, or in some (or all) situations. Anyone who thinks you are isn't worth knowing or caring about. (Quite honestly, if the person who thinks you're lesser for needing mobility aids, then I'd advise looking into some good counseling with someone who has experience working with disabled people. And that goes for anyone who feels that way about needing to use a mobility aid even if it's a matter of only feeling that way about themselves or only needing a mobility aid for things like WDW)
There's also an aspect of fluidity to using aids overall in your life. These days I live in a studio apartment and have at least 4 different mobility aids, 3 of which I use regularly depending on the situation (walker, manual wheelchair, powerchair). It's not a matter of looking at mobility aids as going from one step to another, or even as being particularly "medical", but thinking of them as using the right tool for the task. Sometimes that tool may be a walker or canes, but sometimes it may be a wheelchair or ECV. The right "tool" can change multiple times a day or even sometimes multiple times in one activity/project. When you're somewhere like WDW you don't necessarily have the ability to carry all your "tools" with you so there it turns into figuring out what combination can be carried and/or will give you the ability to do the most.
I do hope you have a wonderful trip! If you can, come back and give us a report on how things go
