Muchova was a set and a break of serve down when she called for a timeout on Rod Laver Arena.
"I was feeling kind of dizzy at some point and almost fainting,” said the 25th seed. “I just asked for help.
"They just checked my blood pressure because I was a bit lost. I was spinning. So they cooled me down a bit with ice, and it helped me."
Play resumed nine minutes later and a revitalised Muchova broke Barty's serve for the first time in the match.
She went on to claim the set 6-3 and raced away with the decider 6-2 to reach the last four.
“I played a bit faster and I was going to the net. I think that was the key by the end," the 25-year-old Czech added.
Disappointment
Barty, the 2019 French Open champion, reached the semi-finals last year, and had been trying to become the first homegrown winner since Chris O’Neil lifted the women’s singles title in 1978.
"It's heartbreaking, of course,” said Barty. “But will it deter me? Will it ruin the fact we've had a really successful start to our season? Absolutely not. The sun will come up tomorrow.”
The 24-ear old rejected suggestions that Muchova had used gamesmanship to take the timeout.
"It's within the rules," Barty said. "She's within her rights to take that time. If she wasn't within the rules, the physios and the doctors would have said so.
Rules
"I was disappointed that I let that become a turning point. I'm experienced enough now to be able to deal with that."
“I’ve taken timeouts myself and after the break I felt like I lost my way with overplaying, overpressing, not letting myself work into the points and really construct points as well as I'd like to."
Muchova will play the American Jennifer Brady for a place in Saturday’s final after the 22nd seed beat her friend and compatriot Jessica Pegula to advance to her second Grand Slam semi-final four months after reaching the last four at the US Open in September.
Semifinal bound 🚨@jennifurbrady95 has booked a ticket for a clash with Muchova as she looks to make the #AusOpen final 🎟️@Kia_Worldwide | #Kia | #MovementThatInspires | #KiaTennis | #AusOpen pic.twitter.com/UG6RCncMXz
— #AusOpen (@AustralianOpen) February 17, 2021
"I hope I make it a habit," said Brady. “Hopefully I’ll have a new habit of making finals."
Brady’s preparations for the tournament were hampered when she was among the 72 players who had to stay confined in their hotel rooms after a passenger on their flight into Australia tested positive for the coronavirus.
“In the beginning of the match I felt the pressure from her,” said Brady. “She’s such an aggressive player and once you give her a short ball the point’s over.
“I felt I was doing a little too much of that. I was looking to just push her back to try to get more on the offence from my own side of the court and then I think I played a really good third set.”
