Decreased bloodflow in the brain

[Luminiferous]

I know bloodflow to the brain essential to function well as it contains oxygen.
However, it seems to me that differences in the quantity of bloodflow has different effects. When I become more active (it feels like there is more blood circulation in the brain during these times), I tend to function much better cognitively.

Is this because the brain receives more oxygen?

What if for some reason, the bloodflow decreases (less bloodflow than normal). Will this leave a permanent damage to the brain?
Because often times, my bloodflow to the brain is noticably low (, a specific part of the brain feels blocked physically), and I become cognitively impaired.

When I explained this to my neurologist, she said that this is probably because of the muscles tensing within my head.

For the sake of theory, let's assume the tension of these muscles decreases the bloodflow to certain parts of the brain. Will this cause permanent damage to the brain in any way?

[imatfaal]

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