With psychiatric stuff it's always a bit of a philosophical question especially if one isn't hearing voices or anything similarly. The criteria for diagnosis is basically whether you are worse than average on some metrics and whether you feel like you have an attention problem - but this could just as well be framed as "the way your personality is".

I've been diagnosed with adhd several times as an adult and every time I scored average/slightly above average on the attention+working memory metrics but scored so high on the other metrics that the ADHD ones were considered out of place!

Personally I don't necessarily believe that ADHD "exists" but am willing to say that I do, in order to take advantage of a prescription for dexedrine which I enjoy. I would of course, in practice, attack anyone claiming it doesn't "exist" because it is counter to my own self interest in maintaining a convenient supply of speedy pills.