When a San Jose couple went on vacation, they left their two dogs with pet sitters, but when they came back a day early, they said it appeared the pet sitters kept the dogs sedated while they were gone.

Fred and Lori Walters used the dog care service Rover.com, which provides independent contractors as pet sitters, to find someone to watch their active Golden Retrievers, Kona and Hudson, during Christmas week.

The Walters said they were wary when the pet sitters declined to meet beforehand. The uneasiness grew when the pet sitters sent photos of the dogs to the Walters as they vacationed.

"Every picture was either sleeping, but literally out of it," Lori Walters said. "Now I think, 'Oh, my God, were they sedated the whole week?'"

The Walters said what really upset them was they came back a day early and caught the pet sitters off guard.

"[The dogs] want to see people, and they're a lot of energy," Fred Walters said. "They didn't even acknowledge me. They came up. They sat down. I put my stuff into the Jeep, and I had to lift Kona up into the Jeep as well. I knew something was wrong."

Fred Walters took the dogs to a 24-hour emergency animal clinic. According to evaluation sheets, a doctor reported that the dogs seemed sedated.

The pet sitters emphatically denied any wrongdoing and referred the Walters to Rover.com.

Rover reimbursed the Walters for the vet bill but did not refund the $1,000 they paid for the service.

Rover told NBC Bay Area it was still looking into the matter, but in a letter to the Walters, the dog care service did not admit any wrongdoing.

NBC Bay Area could not contact the pet sitters, who are still listed on the website as active. In an online post, the pet sitters said the complaint was made up.

The Walters said they hope this will be a lesson for other pet owners.

"If these sitters are doing this to our dogs, are they doing it to others?" Fred Walters wondered.