Coach Brad Childress said Harvin became dizzy when looking up to field a punt and immediately consulted team trainers.
Childress said Harvin came back to the field and was merely watching practice when he fell to the ground and began vomiting. He was in an ambulance 10 minutes later.
"Percy appreciates everyone's concern," Childress said. "He is alert and resting comfortably, but will remain in the hospital overnight."
Harvin missed more than one practice this year and missed a game last season because of migraine headaches. He caught 60 passes for 790 yards and six touchdowns last season, his first in the NFL.