What could cause both people in a car to see everything go white for a few seconds?

A sudden visual change can have medical causes, including fainting or a neurological problem, but a short description from years ago is not enough to identify one. The fact that both people noticed something makes a shared visual or environmental trigger worth considering too. It doesn’t establish a specific explanation.

If anything like this happens again, the driver should pull over as soon as it’s safe and avoid driving until fully alert. Sudden vision loss, confusion, weakness, severe headache, or another episode calls for urgent medical attention.

I’d first look at things both occupants could have seen at once: a strong reflection or glare, a change in the light, or something involving the windshield or vehicle. Those are possibilities to check, not conclusions. A remembered pause in movement also doesn’t tell us whether time literally stopped, since perception and memory can be unreliable during a startling event.

If there are details such as the sun’s position, road lighting, or whether other drivers reacted, those might help narrow down the ordinary possibilities.

Two people sharing an experience is compelling, but it still leaves a lot unresolved. They may have encountered the same external stimulus, and afterward their conversation could have shaped how they remembered it. That doesn’t mean the experience was made up. It just means the account can’t distinguish a visual effect, a momentary lapse in awareness, or something else.