The 'Britain's Got Talent' reject began screaming and weeping in front of shocked families following a performance of 'I Dreamed A Dream' that starred her in Manchester, England.
The classical singer was "very distressed and agitated" as her busy schedule took its toll according to reports.
The 51-year-old - who has mild learning difficulties - is said to have unleashed a "torrent of abuse" at Knutsford Services in Cheshire.
Apparently she needed calming down by a helper and some onlookers filmed the event on their mobile phones.
A friend of Susan's told The Sun: "She wanted to go home as she was tired and upset. Susan is very sorry to anyone she upset."
The former contestant on the ITV talent show has had treatment at the Priory clinic in the past following public outbursts.
Police were not called to the scene and Susan is due to tour with the show until October.
Meanwhile it has been reported that she could return to the show that she came second in four years ago as bosses plan to get her back to perform at the final.