"How do I know if I have a disability?"

I'm having trouble answering this questionnaire when applying for jobs.

I was in the military and given an honorable/medical discharge when I was diagnosed by a civilian doctor with a mild case of narcolepsy.

I don't randomly fall asleep, I don't take medication for it and I have not been legally bound to forfeit my driving privileges or anything else due to the lack of severity of the diagnosis.

I do not really feel it affects my day to day life, and if there are "episodes" then I feel like they've been totally manageable.

I want to be honest but I don't want to have this ruin my chances at good jobs.

How would you answer this question and why?