WASHINGTON — A group of people trying to get the new year off to a healthy start ended up in the middle of a health scare after an incident involving carbon monoxide at a fitness center in Alexandria, Virginia, on Saturday.

At least a dozen people who were working out at XSport Fitness on King Street experienced symptoms such as dizziness and nausea. Several went to hospitals for treatment, Fox 5 reports.

“I started getting lightheaded and I thought it was just the pre-workout actually kicking in,” Al Cavitt told Fox 5. “I looked over to my left and a gentleman literally just collapsed.”

The Alexandria Fire Department says one carbon monoxide reading at the facility showed levels at more than 1,000 parts per million. A reading of just 35 parts per million is considered hazardous, Fox 5 reports.

The incident stemmed from swimming pool heaters, fire officials say.

“They malfunctioned and the carbon monoxide was coming out into the building,” Battalion Chief Mark Dalton told Fox 5.

The fire marshal gave XSport Fitness a citation.