Hull's Kirk Yeaman suffered an epileptic fit at half-time of his side's 52-18 victory over Wakefield at the Rapid Solicitors Stadium on Sunday.
Centre Yeaman last had such a fit 10 years ago.
"It was pretty scary stuff," said Hull coach Richard Agar. "It was nothing to do with the heat and it's purely one of those things that he suffers from.
"He's a bit shaken and tired but OK. He didn't need hospital treatment and he's back sat up and talking, so he's fine."
Yeaman, who is this year's leading Super League try-scorer, managed to watch the second-half from the sidelines in a game Hull had trailed 12-0 at one stage, before recovering to lead 16-12 at the interval.
"We wanted to go out there and perform for Kirk," added Agar. "I thought we finished the game all right and we haven't done that as well as we possibly could have done in recent weeks.
"A 12-point lead can be overcome in the 80 minutes, there's always plenty of changes in momentum in a game and those changes came around."