system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 - Why is it supposedly common to always be tired if you have ADHD?

I see this a lot from adults with ADHD, apparently its common to be tired a lot if you have it? But that seems completely ass backwards to me, given the H in ADHD. Can someone explain?
gpt
Ever spend a whole day in classes, trying to absorb lectures, study for exams, and understand new material?  By the end of the day you're pretty much shot, right?  It's like driving a car for hours and hours.  Even though you haven't been all that active physically, you're exhausted because of all of the mental energy you've had to expend (and the brain uses a *lot* of calories).

Now imagine having to do that, but some asshole in your brain keeps picking up the remote control and flipping through channels.  It takes a *hell* of a lot of mental energy to force your brain back on task, then you panic trying to catch up to what you've missed while your brain was off playing foosball, which leads to more distractions, which leads to more missed material, which leads to *more* panicking. . .it's a pretty vicious cycle.

Expending that much mental energy can lead to chronic exhaustion, especially if the person suffering from ADHD self-medicates through large amounts of caffeine (especially if their method is through soda) and they eventually crash.

Edit: Those of you trying to dispense "helpful" advice. . .if you aren't a psychiatrist, neurologist, or pharmacist, kindly stay in your lane.  Nobody suffering from ADHD needs the advice of "well meaning" but unqualified people.  You're muddying the waters and people suffering from this condition need to seek out help from qualified professionals.