In the book &quot;ADHD Does not Exist&quot; Richard Saul describes Neurochemical Diststractibility&#x2F;Impulsivity(what we call adhd) of two types : low serotoning group and high level epinephrine&#x2F;norepinephrine group.
&quot;The two types described show subtly different symptom patterns.The low-serotonin group tends to look like what people think of when they think of the disorder called ADHD. The high epinephrine&#x2F;norepinephrine group is &quot;consistent in its inconsistency&quot;. Sometimes these patiens can concentrate well, and sometimes they can&#x27;t.&quot;
Maybe this is related to what you say, I see it myself, somedays my brain just works better, I never understood why.