Update: GP has ruled out QT prolongation. She said it's a perfectly valid condition to test for given the symptoms, but the quick ECG she did found QT times that are in the normal range. (a relief...)

She does however see some arhythmia, nothing really dangerous, result was inconclusive, and prefers to have a second opinion from a heart specialist.

Whom I will see tomorrow morning (it doesn't always go this fast, but it's great that I don't have to wait). She also prefers me to ask his opinion on whatever may be wrong and the link with amitriptyline, but if I want to get off it I am free to start tapering.

She also did a blood panel which will be ready tomorrow morning to take to the cardiologist.