It happens to me a lot every day. In my case, it seems to be a combination of
(central) auditory processing disorder (hearing the words clearly or sometimes not-so-clearly due to background noises, dialects and such, knowing the words but not understanding their meaning at that very moment because there's some sort of miscommunication going on between ear and brain),
ADHD (hearing the words clearly, recognising the words but being too distracted by something else to focus on what's being said)
and some type of language impairment (hearing someone talking, not knowing the words or phrases well enough/not knowing them despite them being normal German or English words that I should know/should recognise, therefore not understanding what's being said).
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett