Watson, 22, needed medical attention on court after complaining of blurred vision, nausea and feeling faint during a 6-4, 6-0 defeat to Bulgarian Tsvetana Pironkova.
The world No38, who went into the year’s first grand slam in buoyant mood having won her second WTA Tour title last week, suffered an illness later diagnosed as glandular fever in Melbourne two years ago.
It stymied her ascent and hampered her entire season and, though the circumstances and symptoms are familiar, Watson believes it is a recurring problem and not the viral infection.
“I get this at different times. I have a day or two here and there where I feel like this. I’m going to see the doctor afterwards because I can’t let this affect me any more. I’ve lost this week now,” she said.
“I felt very light-headed and low on energy. I think it’s just one of these things that I have, girl things. It just happens.
“It was actually the same doctor that came on court when I called the trainer for no energy two years ago. When he came on in 2013 it was the same thing.
“He said: ‘We’ll just do the same, give you some gels and you’ve just got to fight through it.’ I tried to play more aggressive so we wouldn't have too many long rallies, but I wasn’t consistent enough.”
On a bad second day of the grand slam for Britons, James Ward and youngster Kyle Edmund both limped out in the first round.
British No2 Ward put up a fight in a four-set defeat by 31st seed Fernando Verdasco, while Edmund lost in straight sets to American Steve Johnson.
World No1s Novak Djokovic and Serena Williams both progressed to round two without dropping a set, as did men’s defending champion Stan Wawrinka and women’s fourth seed Petra Kvitova.