Suffering from dehydration and with her legs cramping severely, 33-year-old marketing consultant Smyth reeled grotesquely as she neared the line but willed herself forward to finish seventh.
Smyth fell backwards over the line after crossing it but somehow pushed herself forward to cross it again, waving away officials as she did so.
She then collapsed and trackside officials picked her up and carried her away for treatment.
Australian chef-de-mission John Devitt said Smyth was placed on an intravenous drip for 90 minutes to replace lost fluids and soon recovered.
''She's now a hundred percent,'' Devitt told reporters. ''They got fluids into her immediately and rehydrated her.'' Australian media carried photographs on Monday of Smyth sharing a drink with friends at a Melbourne hotel several hours later.
''To be honest, about the only thing I remember was the roar of the crowd,'' Smyth told The Age newspaper, admitting she had been hallucinating as she neared the finish.
''I actually thought the finish line was moving,'' she said.
Australian Kerryn McCann defended her marathon title after a memorable battle with courageous Kenyan Hellen Cherono.
REUTERS VJ RAI0655