A former safety driver for Uber’s autonomous vehicle program revealed that he suffered a mild concussion while operating one of the company’s prototypes.

During a recent interview with Business Insider, Ryan Kelley detailed some of the poor working conditions Uber safety drivers experienced prior to the program being halted after a fatal crash earlier this year.

According to Kelley, there was one day during December 2017 when the Uber prototypes were prone to overly aggressive braking. Kelley said he experienced blurred vision and an upset stomach during the day as it was similar to “being in a series of low-end collisions for three hours, with my head slamming against the headrest constantly.”

Kelley and other drivers told supervisors of their headaches, but the manager responsible for safety, Rob Shoup, allegedly brushed aside their complaints and accused them of faking symptoms.

After making a trip to the emergency room later that day, Kelley was diagnosed with a mild concussion “consistent with symptoms for a low-speed car accident.”

In addition, Kelley told Business Insider that Uber strongly encouraged drivers to avoid taking bathroom breaks because stopping a test vehicle could require up to an hour for rebooting and troubleshooting.

Kelley was ultimately fired on January 26 with Uber claiming that he had rolled through a stop sign on January 3 and not reported it.

“I truly believe I was let go because I was a squeaky wheel. I made safety concerns,” Kelley countered.