Op, thank you so much for starting this thread and to everyone who has posted. I have long thought I was a little weird, so your contributions are like a wet flannel to a fevered brow. I'm a name changer because I'm embarrassed at some of the confessions I'm going to be making here.
I'm getting on a bit now, and I've always been like this. In fact, a few days ago, I asked for this for Christmas:- www.etsy.com/uk/listing/889241946/metal-wall-sign-plaque-dear-brain-please?ref=shop_home_active_130 
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My working life requires a fair amount of brain power and, when required, I can concentrate for hours on end without stopping for food, and sometimes even for drink. I will admit to finding this extremely satisfying although, nowadays, if I have too many days like that on the trot, I'm exhausted!
The rest of the time, I struggle to concentrate on one thing at a time due to Radio GaGa playing full blast - monologues and dialogues and hypotheses and sketch plans etc. Lots of colour and sometimes music, bits of poetry and prose, film scenes, art, concerns about the planet, how to rearrange the furniture in the lounge, how the kids are going to get on the housing ladder, what to buy DH for Christmas.
This means that many things, be that a work related task or doing something in the house or garden, take longer than they should as I complete only half the task before my brain suggests, very firmly, that I should be doing something else. So off I trot to do something else, leaving a trail of things which are almost, but not fully, completed.
I hate mess, and this causes mess, and then I have to spend more time clearing everything up, in order to give myself some chance of clarity of thought. (I'm currently looking at my very untidy desk and thinking that I am going to have to clear it up before I start work later on today).
It is much, much worse when I am stressed/under pressure and that's when random words come out of my mind which have absolutely nothing to do with what I'm thinking. When the children were small, for reasons I won't bore you with, I was massively stressed and the talking to myself was at its worst, particularly when I was driving and was concentrating on that. I would say things like "I love you", "I hate you" "Stupid woman" (presumably about myself) and "I want to go home" (I live many, many miles away from where I was raised). I realised how often I must have been saying that when DC2, who was strapped in his car seat in the back of the car came out with "I want to go home" as one of his first fully completed sentences 
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Like many of you, I tend to have spectacular dreams, full of colour and action. I once drempt an entire short play, complete with plot, characters, and dialogue. I found the ending so upsetting, I struggled not to cry when I was explaining it to a friend. I only wish I had the talent to write it up.
I have also suffered from sleep paralysis and very occasionally accompanying hallucinations. More recently, these are auditory - such as humanoid moaning or things being dropped on the floor.
However, the most embarrassing bit is the images I have used to get to sleep over the years. During the period of extreme stress I mentioned above, I could only get to sleep if I envisioned myself barefoot, dirty and in rags with my hands bound behind my back, kneeling before some unseen oppressor. It was as if it had been videotaped and was on a repeat cycle. Looking back at it, the point of that image appeared to be that this was the lowest point and I was going to get myself back up off the floor. Has anyone else had anything like this?