EDEN PRAIRIE (AP) — Minnesota Vikings wide receiver Percy Harvin was taken to a hospital by ambulance after collapsing at Thursday’s practice, and coach Brad Childress said Harvin suffered another migraine headache attack.

Harvin, who has dealt with migraines most of his life, has been unable to practice for most of training camp because of the headaches and their debilitating symptoms.

Harvin returned to the field on Monday after missing more than two weeks, but at the beginning of Thursday’s workout he experienced another episode that was scary enough for the Vikings to halt practice while their teammate received medical attention.

Childress said that Harvin’s episode was triggered when he looked up into a mostly cloudy sky to field a punt during a special teams drill. Harvin went inside to see team physician Dr. Sheldon Burns, then came back out to the field.

At that point, Harvin doubled over and was seen trembling, before players and coaches stood in front of him for privacy while reporters watched from a distance.

“I don’t know how they classify it,” Childress said. “Not really a seizure, but he had some trouble over here. I’d be remiss if I tried to qualify it one way or another. It seemed like he was stable.”

The Vikings continued with practice for about five minutes while Harvin was being worked on, then drills were stopped while the situation was sorted out. After Harvin was loaded into the ambulance, the Vikings gathered on the field and took a knee in prayer. They resumed their work for a few more minutes before calling practice over at least an hour early.

The ambulance did not leave right away after Harvin was loaded, and it left without sirens sounding or lights flashing. Though the situation didn’t appear grave, it was clearly somber.

“Obviously that one hit, and it hit hard,” Childress said. “It’s always scary for all of our guys when you see a teammate struggling with whatever.”