EDEN PRAIRIE, Minn. -- Percy Harvin experienced the scariest episode yet in a career plagued by migraine headaches when he collapsed at Minnesota Vikings' practice Thursday and was taken to a hospital by ambulance.

Coach Brad Childress left team headquarters after practice and spent the rest of the afternoon at the hospital with Harvin, who also got visits from other coaches and teammates.

"Percy appreciates everyone's concern," the coach said in a statement posted on the team website Thursday evening. "He is alert and resting comfortably, but will remain in the hospital overnight."

Harvin, who has dealt with migraines most of his life, returned to the field Monday after missing more than two weeks, but at the beginning of Thursday's workout the wide receiver experienced another episode that was scary enough for the Vikings to halt practice while their teammate received medical attention.

"To see a guy go down, it's never a good thing," defensive end Ray Edwards said. "Just pray that the Lord is with him and he gets back to us safely, and to his family most importantly."

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.

Soon after, Harvin was seen doubled over and trembling. Players and coaches stood in front of him to shield him while reporters watched from a distance as Harvin received medical attention.

"I don't know how they classify it," Childress said after practice. "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."

Childress added: "I'm putting it in a migraine category, just because of what preceded that, but I certainly don't know what put him down on the ground over there, if it was some kind of reaction or what."

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

"It was an eye-opener," running back Adrian Peterson said. "It's been tough for him. I just encourage him the best way I can."

The ambulance did not leave immediately after Harvin was loaded, and it left without its siren or lights on. Though the situation didn't appear grave, the mood was 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."