I got confirmation of something I suspected. In 2012, I experienced a great deal of
this dizziness-when-rising (which bears the fancy name "orthostatic hypotension") back. It stopped when I stopped a medication. I learned today via the internet and then, independently, from the doctor, that the medicine I took then (but do not need now) has a side effect of increasing one's susceptibility. Hence, when I stopped taking that medicine it was natural that the condition faded.
Today "no news is good news". I did miss most of the afternoon's work, but was able to return to my office in time to get some things done. All told, color me relieved.
I did not even mind when the bluebirds in the park proved difficult to photograph.