R.J.
The first half you described (including mood swings), you realize, is TEXTBOOK ADHD-i (adhd-inattentive), right?
Best online source there is www.additudemag.com, but the hands down best book I can recommend is "You Mean I'm Not Lazy, Stupid, or Crazy?!?" by Kate Kelly and Peggy Ramundo. I recommend it to parents all the time, but it's actually for/about ADHD in adults. Written by people in the field who actually HAVE ADHD.
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As far as meditating? Eh. If you have ADHD then it's unlikely to help much. Most people have to expend energy to think... and their natural resting state is completely clear. ADHD types have to expend energy to be clear headed, and our natural resting state is with 5 or 6 thought streams (or more) constantly running. So for neurotypical people meditating helps them clear away the thoughts and focus in the present. For ADHD people, it's hit or miss, and more often... miss. Or actually makes things worse.
One thing SIMILAR to meditation that helps most people with ADHD is "switching gears". That means NEVER (if you can help it) switch from one activity to the next. INSTEAD, take a 5-10 minute break between activities to 'transition'. Go sit outside and stare at the clouds. Go to the bathroom and daydream. Sit in your car and listen to music. Read a chapter in a book. SOMETHING that creates a "line" or "space" / "switch gears" between one activity and the next. Sort of like walking down the halls between classes. It gives our minds a chance to wrap up and move on... instead of just tossing one more, and one more, and one more ball into the juggling until you're so crosseyed you shut down and just turn inward.
Personally, I like going outside. First got into the habit smoking... but I still do it even now that I'm not smoking. If I don't take the time to switch gears, before long, I can't even SEE the world around M.... because my mind is spinning too much, so I end up turned inward and just 'going through the motions' with my body. Heck, sometimes I can't even go through the motions. BUT if I head out to my porch, and just sit and prep myself for the next "thing" to do (and start that mental rolodex spinning) then I can pop up! and move onto the next thing fully engaged.
So it's LIKE meditation... in that it's clearing one's mind. But it's a LOT shorter (just a few minutes) and fairly constant... and OPPOSITE of meditation you TRY to think instead of trying not to think. Think of what's coming up next (okay... dinner, or okay... shower and get dressed, or okay... bills, or okay... lay down and play trains).
TIMEOUTS are also part of the coping skill set of most ADHD types. We have VERY intense emotions (higher highs, lower lows, and looooooonger capacity. Most people only feel something for a few seconds and it starts to fade. ADHD types tend to feel full on for minutes to hours, until another emotion also at full strength, replaces it), and we can hyperfocus on them... which is something like a spiral. Feeding off of itself. Timeouts allow us to shift gears EMOTIONALLY. Start getting snippy, horny (with nothing to do with it), no patience, embarrassed, sad, etc.... head back outside (or wherever) and take a 5 minute sanity check and get the happy back.
As a side note to both changing gears & timeouts... ADHD types tend to get VERY cranky when we CAN'T change gears. Because it's exhausting and frustrating to have so many things going on mentally, without the chance to table them. You may find simply switching gears between tasks will actually reduce a lot of your general frustration.
Assuming, of course, that the giant flashing neon sign saying "ADHD-i" in they mental hyperactivity... does mean you're ADHD-i or ADHD-c (c is combined adhd-i and adhd-h)