Eriksen suffered a cardiac arrest towards the end of the first half of the game between Finland and Denmark before being resuscitated.
On Tuesday, Eriksen said he felt "fine -- under the circumstances," adding that he would remain in hospital to go through health examinations.
"That picture that I still have in my head, that's so disturbing. You really feared the worst," Sparv, who is captaining Finland during the country's first major tournament, told CNN Sport's Patrick Snell.
"You thought that he was going to die. It was very, very emotional and we're just so happy and glad that he's doing fine."
Sparv added that some of his teammates were understandably emotional after witnessing what was a "very traumatic experience." For his part, he said his first action after the game had been suspended was to switch on his phone and text his family.
"I wanted to be in touch with them. They were of course worried as well," said Sparv.
The match eventually resumed with Finland winning 1-0, but the decision for the teams to keep playing has come under criticism, notably from Denmark forward Martin Braithwaite.
According to Braithwaite, the teams were given two choices by UEFA, European football's governing body: to finish the match there and then, or to play the next day at noon. The first option, Braithwaite said, was the "lesser of two evils."
"I don't think it's the optimal solution to play football after an incident like this. I don't think it's mentally healthy for anyone to go back out on the pitch and play a game of football," said Sparv.
"We had two bad options ... I don't think that it would have been any better going back to the hotel, sleep, and go back to the stadium the following day ... I don't have any answers, I don't know what a sensible alternative would have looked like.
"Should the game have been canceled? Should it have been a zero-zero draw, both teams get one point? Maybe that's something."
In a statement to CNN, UEFA said it is "sure it treated the matter with utmost respect for the sensitive situation and for the players ... The players' need for 48 hours' rest between matches eliminated other options."
'A fantastic footballer'
Having spent many years with Danish club FC Midtjylland, Sparv knows how important a player of Eriksen's caliber is for football in the country.
Currently playing for Inter Milan in Serie A and previously for Tottenham Hotspur in the Premier League, Eriksen has won more than 100 caps for Denmark over the past 11 years.
"[He's] a fantastic ambassador for Danish football," said Sparv.
"Just the way he plays, he's a very technically gifted footballer. It looks so easy, he has a fantastic first touch, his vision, his goal-scoring ability -- he's just a fantastic footballer.
"I've met him on a few occasions, I've played against him once or twice and he always comes across as a very humble human being."
While Denmark continues its Euro campaign against Belgium on Thursday, Finland plays Russia on Wednesday.
Sparv admitted that preparing for the next game -- while still coming to terms with the last one -- has been a struggle.
"It's been so many different kinds of emotions at the same time," he said.
"For us, it was a big occasion, it was the first time we participated in a major tournament, our first game. We won that game. It should have been like this major thing in Finnish football history, but our celebrations were very subdued.
"Usually there's a lot of music and dancing and laughing in the dressing room after a win. But we were just sitting in our places, trying to reflect on what had happened, trying to read some information on our phones, trying to figure out: how is Christian doing?
"It was not the kind of joyous moment that it normally would have been, which is quite natural I think ... when you think about a player nearly dying, I think it puts things in perspective."