I think I may have ADD. Now, I've heard some people say that ADD doesn't exist, that it is simply a behavioral problem and nothing more. Maybe. But, whether the problem is truly neuro-chemical in nature or simply due to social constraints and outlook that doesn't change the fact that it is a problem, now does it?
Count me in as one of those that was an absolute skeptic regarding ADHD/ADD. I think I even posted such in this forum. Especially, when it came to medicating the "symptoms".
It's a complicated story, but my 12 year old daughter has been diagnosed with ADHD-combination type (both hyper-active and inattentive). And it looks like my son also has it. My daughter has a very complicated medical history so there were many things that had to be ruled out first. (i.e., brain injury from chemotherapy due to cancer treatment). It tends to run in families that have a high amount of depression, alcoholism, and drug abuse.
ADD or ADHD symptoms generally are evident from childhood because it is a brain disorder. So, I don't think adults can "develop" it. But, don't quote me on that. I'm still learning all that I can about it. Generally, someone with ADHD can become depressed because they have such difficulty functioning in life. But, depression is not the core problem. It's a result of untreated ADHD.
The diagnosing of ADD/ADHD is not a exact science. I would find someone who is extremely experienced in diagnosing and treating this disorder. They, most likely, would be able to determine whether or not you do, indeed, have it.