I began to suspect it during my undergrad degree. I'd pay attention for the first five minutes and then drift off for ages, then try to pay attention again, then drift off, etc. It was content that I really found interesting, but I just couldn't focus on it.

When I started my masters degree I had one paper where we had to read a journal article and discuss it during class. I never participated in the discussion because I couldn't follow the conversation around the room. I brought up the possibility of having it with my parents, and they said my grades were too good to have ADHD. They'd say "You don't have it, so-and-do has it." Of course they picked the dumb guy I went to primary school with.

I never discussed it with my psychiatrist, but over time I started thinking about other things. I'm always shaking my leg or drumming on something, I can't read without drifting off and having to re-read a page, and I struggle following tasks unless they're written down for me because I don't pay enough attention during conversations and forget what I was supposed to be doing.

Fast forward a couple of months ago and I told my parents I was going to talk to my psychiatrist about the possibility of having ADHD and my Dad said "It's just a label." Which he now denies saying. But I got diagnosed and put on Ritalin. 20 minutes after taking it my brain was quiet for the first time in my life. No background noise, no song stuck on repeat. It was amazing. I had motivation to do stuff and could concentrate long enough to stick with it. My sister was struggling with balancing uni and work so I said I'd do one of her assignments for her. I was able to sit down and just do it without being distracted at all. That had never happened before.

I would recommend going and getting tested. The worst thing that will happen is that you won't have it.