Sounds like a horrible diet, which could cause a lot of problems, including low potassium (and long
QT), anxiety, low magnesium (and long
QT), vitamin defiency, etc. You need at least 3000 mg of potassium daily, and preferrably 3.500-4.700 mg (guidelines vary between countries, in Norway it's 3.700).
I think your prolonged corrected QT interval was caused by 1) Mathematical overestimation from the Bazett formula due to a high heart rate, and 2) Low potassium.