I was diagnosed as an adult (when I was 33 years old) shortly after my son was diagnosed (both of us by his pediatrician, who was a family friend). I had really been struggling for a very long time and was getting less than 4 hours sleep at that point in my life. I attributed it to parenthood, stress etc. and really was initially surprised to realize I had ADHD.
But truth be told, societally, I think many people that complete those questionnaires would come up as having the potential to have ADHD because we all live so frenetically these days. We are being programmed to have short attention spans and we are eating so may things that are deteriorating our brain chemistry and accelerating inattention as well.

I think you have to look at the extent to which it could be affecting your life if you do have ADHD and then what you think might help you make a plan to make things better.
My son and I briefly tried some Cognitive Behavior Therapy and other behavioral modifications, but in the end, we both needed medication to be successful. I have been successfully medicated for 17 years (under the care of a psychiatrist) and am so much more productive with it. But I am still not medicated for about 10 hours a day and sleep mostly between 5-6 hours a night (sometimes 7 if I am sick or just exhausted).

The important thing is if you feel you DO have ADHD and if it is impacting your life in a significant and negative ways, identify the areas where you need help. Meet with a physician and discuss making a plan to address those problematic issues and develop a plan together. Self-diagnosis can be fine, but if you feel you need treatment, I would go see a doctor. Remember if you do have ADHD, it is often a journey to find the right strategies, medicines and coping mechanisms to address your personal challenges. Also, it helps to realize that medicine, alone, is never a complete answer. But for me, it has been a gift, because with medicine, I can focus to do the work and follow through with my plans to address my challenges and make improvements in my life.

Good luck on your journey.