Fainting should always be investigated!
An unexplained faint or blackout is a major red flag. Fainting can happen due to an arrhythmia so you shouldn't ever let a doctor tell you it is normal to faint. It isn't.
Long QT Syndrome can cause fainting and seizures and sudden death
Fainting occurs when the heart temporarily beats in an unorganised way which means it doesn’t pump blood as efficiently as normal and blood pressure drops.
When less oxygenated blood reaches the brain it can cause dizziness, confusion, blackouts and seizures. The brain is extremely sensitive to blood flow.
Unexplained fainting = See a doctor.
This Ecg picture is Isla's. It was a short run of Torsades while lying in a hospital bed so she remained conscious.
Even a few seconds of Torsades de Pointes can cause a faint.
Above, Isla may have felt dizzy but not lost consciousness as it was only a few seconds. It would most likely have to be around 5 seconds of Torsades before someone faints.
Over 30 seconds of Torsades and the rhythm may descend into Ventricular Fibrillation, which wouldn't self resolve and definitely needs a shock from an AED or ICD to recover.
The time frame of Torsades