The Romanian two-time Grand Slam winner was visibly struggling as the temperatures hit 33 Celsius (91 Fahrenheit) on Rod Laver Arena.
She kept going but lost the gruelling fourth-round clash 6-4, 3-6, 6-4 in 2hr 33min, red in the face and frequently bending over to try to catch her breath.
"I have no injury, this is good. Only the heat got me actually early in the first set. I felt sick, felt a little bit dizzy," said the former world number one.
"It's tough to play in the heat, and I was not ready today. She was a little bit stronger, and that's why she could win the match.
"I was close to just giving up, because I was exhausted, how I looked, actually.
"But I felt like she was starting to miss, and I just stayed there. I fought for every ball. But with not much confidence."
The fit-again Halep came into the tournament full of confidence after her first title in 16 months at the warm-up event in Melbourne.
It followed a truncated 2021 season when she struggled with calf and knee injuries.
Despite losing, she said there were a lot of plus points to take from her start to the year.
"I'm super happy with the way I have been here in Australia. I struggled a lot last year, and the way I got up, it's looking really good," she said.
"I'm happy about that, and I will take only the positives."
