Heather Watson admitted a slump in energy levels was to blame for a first round defeat at the Australian Open.
The British number one arrived in Melbourne brimming with confidence, after capturing her second WTA Tour title at last week's Hobart International.
But she lost seven straight games, going down 6-4, 6-0 to Bulgaria's Tsvetana Pironkova, a former Wimbledon semi-finalist who is ranked 14 places below her.
And for Watson, who called the doctor to the court at the end of the first set, it was a worrying reminder of two years ago in Australia, when she felt the first signs of what would become a bout of glandular fever that sent her world ranking spiralling to 162 and derailed her 2013 season.
"I woke up and didn't feel that great, I just felt bloated and weak and didn't have any energy on the court," admitted the world number 38.
"It's really frustrating but it happens. You're dealt with different cards on different days and I should have done better. It's a real shame and it sucks. It's tough at this level when you are fit, it's impossible when you are not."
Watson insists she will now seek medical advice as she looks towards a season in which she hopes to push further up the world rankings and go beyond a Grand Slam third round for the first time.
"I get this at different times and it's something that I have to understand better. I have a day or two here and there where I feel like this," she added.
"When the doctor came on court I saw he was the same guy that treated me in 2013. There wasn't much he could do."
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