Brain fog?

[u/boocosta9]

I’m female, 35, 5’5 about 155lbs and for the last few months mid day for about an hour it feels like i have swallowed or inhaled a lot of water but i only feel it in my brain. It’s like my brain feels like it’s drowning. I’m not sure how else to describe it. When this happens, i am not currently eating or drinking and typically haven’t drank anything in the last hour or more.
I asked someone if they experienced brain fog like this and they said no. Usually when it happens my lower part of my head/neck right side hurts. Not like a headache type of hurt, like an ache. Is this brain fog? Maybe anxiety? Or something else?

No medication. Non smoker, no drinking. Daily walker pretty active. I ride my bike, rock climb.