I had on several occasions the same thing happen to me laying on my back under the Model A and the 53 Buick. Extreme dizziness but only when I was looking straight up. When I would roll over it would go away after a minute or two.
I found out that it was caused by particles in the inner ear being in the wrong place in the canal. The attached "Foster Maneuver" cured it.
https://www.webmd.com/brain/home-remedies-vertigo#2-4