Years ago flying cancelled checks in a 210 I got caught in a couple embedded level 4. I thought that was going to be my last flight. The controller gave me a 2000 ft block of airspace, then it turned into just do your best, no one else is in the area.
It was so rough that my car keys came out of the pocket of my flight bag and lodged in the ear piece of my sunglasses. I could not let go of the controls to remove them. It didn't matter because a minute later my headset and sunglasses departed. My flight bag, the only thing not strapped down, was flying all over the place.
I never went inverted, but there were several times I was 90 degrees and falling. I hit my head on the yoke a few times, as well as the side window. The stall horn was sounding pretty much continuously no matter what my indicated air speed was. I am not sure if I was along for the ride for 5 minutes or 5 hours, but pretty sure it was only about 30 minutes.
The controller was really glad to hear from me when I was finally able to get my headset back on. I quit that job several times during the ride, only problem was I still had to get back to the airport where my truck was parked.