Harawira-Naera says he is "on the mend" but "not in the clear yet" and will undergo further testing to get to the bottom of the frightening incident at Sydney's Accor Stadium.
Shortly after taking a hit-up in the second half on Saturday night, Harawira-Naera appeared to become disoriented and fell to the turf.
The match stopped for over 10 minutes as medical staff rushed onto the field and attended to the New Zealand international, who had begun convulsing.
Harawira-Naera was conscious and responsive by the time he was transported from the field in a medicab amid a standing ovation from the crowd.
Harawira-Naera travelled by ambulance to Westmead Hospital with his sister, who was a spectator at the game.
The New Zealand international was discharged around 3:30 on Sunday morning and shared a video update on his condition about eight hours later.
"I'm back on the mend, not in the clear yet but we'll get some more scans and sort it out," Harawira-Naera said.
"Health comes first but I'm obviously hoping to get back on the field as soon as possible as well."
Harawira-Naera thanked those who showed support following the medical episode.
"I've been pretty fortunate to receive a lot of messages about what happened last night," he said.
"I'm doing a lot better now, so love to you all."
No player harboured more concern for Harawira-Naera on Saturday night than teammate Albert Hopoate, who roomed with the second-rower for three years.
The pair are close mates, FaceTiming or catching up most days, and the Raiders winger was visibly distressed when Harawira-Naera went down.
"Obviously it was pretty scary at the time," Hopoate told AAP.
"You don't expect anything like that to happen, especially in a game. There aren't many words."
Canberra captain Jarrod Croker abandoned all thoughts of the contest as his teammate lay on the ground.
"For that whole period, I don't think anyone was thinking about football, to be honest," he said.
"Everyone was just looking out for Corey and doing whatever we could."
Raiders coach Ricky Stuart praised both his players and South Sydney's for rushing to Harawira-Naera's side after he fell.
The players encircled the 28-year-old to give the medical staff privacy as they worked on him.
"That's when you see the real character of these footballers," Stuart said.
"When one of the boys go down, it doesn't matter what team he's on, everyone got around the fact that it was a serious situation.
"There was a lot of care out there for him. That's appreciated by all our players and club, how the Souths boys handled it as well.
"No one likes to see those serious types of scenes."
The Raiders regrouped after Harawira-Naera left the field and vowed to keep playing in his honour, eventually triumphing 33-26.
"Jarrod Croker, he's our leader and Jamal Fogarty, those two are pretty good leaders and they always know what to say in moments like that," Hopoate said.
"We got in a huddle after that and said we'll do it for Corey, and we did."
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