Matthew Moczygemba knew something was wrong when he lost his thirst. It was midafternoon on a 103-degree day in Fort Worth, Texas, and the UPS driver had been delivering packages for several hours. Soon he felt dizzy, then he pulled his truck over and vomited onto the curb.

“I stopped sweating and was starting to get cold,” said Moczygemba, 35, who has worked for UPS for five years. “It was a bad feeling.”

Moczygemba wound up at a hospital emergency room, where doctors diagnosed him with dehydration and heat exhaustion, and gave him several bags of IV fluid, according to medical records. 

He was released a few hours later, but he has not returned to work in the nearly three weeks since. 

“I’m nervous about going back,” Moczygemba said.