Your question of “Do I really have something that is real?” is an almost universal question until people can wrap their minds around the subtleties of the ADHD nervous system. The diagnosis is rock solid and one of the few times in life that we can say Always and Never. The difficulty is that there is nothing we can pull out and say, “Ha! See! There it is! ADHD.” There is no lab test or scan we can show people (or ourselves) to prove we have ADHD. Instead it is an understanding that you have based on your ability to look back over your entire life and see the unchanging pattern that is an ADHD nervous system.
The hallmark feature of ADHD has always been the inconsistency. Inconsistent engagement, inconsistent performance, inconsistent moods, etc. Activities that were done beautifully yesterday are terribly done today. Usually this is presented in a very judgmental way that the person with ADHD is “flighty, unreliable, unpredictable, or intentionally not trying.”
It is only in the last few years as children with ADHD became articulate adults with ADHD that we have come to understand that there is a consistent pattern to the inconsistency. In a limited number of circumstances people with ADHD could “get in the Zone/get in the Flow” and not have any impairment at all. When an ADHD person is Interested, Challenged, or finds the task Novel or Urgent they snap into the Zone and can literally do anything they try to do. When they lose that sense of ICNU, they are back in LaLa land again. The conditions that engage, organize, and motivate the other 90% of human beings (Importance, Rewards, and Consequences) never ever work for people with ADHD.
So here is where the certainty comes from. People with ADHD nervous systems ALWAYS use Interest, Challenge, Novelty, and Urgency and can NEVER use Importance rewards and consequences in daily life to get the tasks of their lives done.
The second defining feature of ADHD is like the first. People with ADHD nervous systems ALWAYS have an intense, almost catastrophic emotional response to the perception that someone has withdrawn their love, approval, or respect and non-ADHD folks NEVER do (or at least not to the disruptive extent that ADHD people do). Rejection Sensitive Dysphoria and an Interest-Based Nervous System together can explain virtually all of the manifestations of ADHD.
So, in the end the only person who sees the evidence of ADHD first hand is you. In the end the only person who must completely be sure that you have an ADHD nervous system is you as well.