The woman apparently fainted and fell onto the tracks at the 59th Street 4/5 platform on the East Side just after 7 a.m.
She was helped off the tracks by officers and commuters and taken to the hospital to be treated.
She was not struck by a train.
Service on the 4, 5 and 6 trains was briefly affected.
The MTA says the line was quickly running with good service after some delays.
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