I do not experience this.
I seem to have bursts of thought, interspersed with periods of vacancy or *space*.
I will start thinking about something, and fixate on it, thinking intently, obsessively.
Then just as quick as it started, it will end, and I find myself drifting, not thinking about anything in particular, *spaced out*. Then I snap out of that, and it's back to analytical and obsessive thinking again.
I have some vague theories as to why this is... lack of sleep, prior substance abuse, anxiety... But I don't really know for sure.
I think there are some correlations between AS and incessant thinking. But I've known other people, not on the Spectrum, who often complained of, "not being able to turn their brain off", or just thinking constantly, to the point where it interferes with sleep.
I believe this is just a trait some people have, not necessarily indicative of autism.
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Plantae/Magnoliophyta/Magnoliopsida/Fabales/Fabaceae/Mimosoideae/Acacia