As a chronic migraine sufferer, I can say for most people ~ you either do suffer from low PWM, or you not.
However, in fact, all humans suffers from low PWM flicker. Once, I complain to my coworker about being sensitive to low PWM flicker and thus I could not look at iphone OLED screens. He immediately dismissed this and claimed its just a made up theory. Then, I proceed to show him a slow motion video recording of a room with fluorescent light. The PWM in the video was a 20 hz flicker btw. I asked that he look at the video for a couple of minutes. Following that, he himself complained of eyestrain, nausea and migraine. I replied yup, that's exactly how I felt when I look at iphone oled screens.
The problem is that the definition of "low" PWM varies from individual to individual. According to a number of studies, most people should not have symptoms of above 50 hertz flicker. To many, below 50 hz is low PWM. There are studies though that showed anything below 3000 hz may still be detectable by a number of people. However, if you are really sensitive to PWM, even 25000 hz flicker may even give you a mild migraine.
Some panels uses PWM to control screen brightness while at the same time use a secondary backlight that flickers at a constant 60hz.