Turn signals ‘indicators’ flash using a relay (in older vehicles), or are controlled by electronics (the circuit is sometimes buried inside one of the vehicles control units). The relay or control unit, turns the signal lights on and off when power is applied.
If a lamp has broken, or a lamp has been changed for a different type (e.g. an LED). The load on the circuit can change. This can cause the indicators to flash faster (hyper flashing).
Can be found on this page: My Turn Signal (Indicators) Flash Fast on One Side?: (Opens in a new window / tab)