I'm so glad I found this forum!!! I've been counting letters in words in my head really fast since I was probably 14 years old. And Koala, like you, my favorite number is also 12. It's the perfect number. I can break of words/phrases into groups of 1,2,3,4,6,12! So many possibilities! Also, when counting small phrases in my head, I love it when there are 3 words that have 3,4,and 5 letters in order. For example, "The girl cries." Three words, whose letters all add up to 12, and are in consecutive order, 3,4,5.
Also, I haven't seen anyone post about this, but I spell with numbers. What I mean by this is I think of letters in my head and visualize how they would be spelled with numbers. For example, the letter "a" is most closely resembled to a digital 2, letter "b" is a 6, etc.
Like everyone else, I kept this to myself for a while, and then recently started to share with friends and coworkers and they get a kick out "testing" me and throwing words out at me to count. I do find this mentally exhausting as well and wonder if maybe that is why I constantly have tension in my neck and shoulders, because I can never really get my brain to rest. Has anyone ever taken medication for this? Seen a professional? I'm curious to know whether it's something I should take care of now (I'm 24 years old) and if it will get worse when I'm older.