If you feel you need a placard, by all means get one. If I see someone who is not visibly disabled but has a placard, I am not going to question the necessity of their having one. (What I do object to is someone without a placard parking in a handicapped spot.) If you have a legitimate reason for a placard, don’t worry about what other people think. If you need one, you need one, and you don’t owe anyone an explanation.