A year or two ago I suddenly found that one particular action in our house brought on a sudden, slight feeling of dizziness for a few moments - nothing else did it, just that one thing: opening a below-sink cupboard door and dropping rubbish into the bin that swings out, then looking up again (onset).
I was of course puzzled and, together with giving it some careful thought, I did a bit of poking around on the internet. Fairly early on I began to suspect it was something to do with the inner ear. Then it started happening in a single other set of circumstances: as I did a sort of 90 degree twirl around a pole at the door of a bus on my way out of it.
I am not on any medication, I do not have low blood pressure or arthritis.
I settled upon a small piece of information and started in every case to do the following whenever the experience returned: I jerked my head as sharply/rapidly back as I could, right back. The sensation stopped very abruptly in every single case (very occasionally I had to do the remedy a second time).
In the case of the bin I had noted that because there is a large window with a wide view beside the sink, I am inclined to be looking out (straight ahead) as I approach and open the bin. Then I suddenly look right and sharply down at the bin for an aim, basically as if I were looking down at my toes. The twirl at the pole on the bus is something that has an effect one can simply picture in light of the information that caught my attention. I have not experienced this since about three months after I first "took up the habit".
Have a look at references to crystals in the inner ear, Google will do. Your acquaintance might like to try the trick but otherwise if he remains concerned he probably should seek medical advice.