> Why spend the energy masking in the first place?

Because of things like this:

Coworker: "How are you doing?"

Me: "Bad."

The conversation, and the rest of my day, does not significantly improve from there.

Does that example really require masking? Absolute not. You don't have to lie when you provide a neutral response. Examples: "Busy day", "Just feeling tired", "Many things to get done.". Those are not necessarily good or bad and suggest you aren't making small talk.

Or, if you provide a never ending story they will see your disability for what it is and they won't ask you a second time.

I'd say that's not masking, since literally everyone does it. As a famous comedian that I can't quite place right now once said, (paraphrasing) "the only valid answers to "how are you doing?" are good, fine, or okay.

Honestly, some things like this are solved with learning certain skills, practicing them a bit, and then it becoming easier. Answering to "How are you doing?" does not require masking, people asking it in casual contexts usually do not expect any kind of "honest answer". It is as hard as answering "hi" to "hi". There are plenty neutral answers that neither require you to smile and play it happy, not invite some long, awkward conversation. It could also depend on where you live though, of course.