Self-healing is a feature in Film type capacitors. Self healing is a process by which pin-hole defects in the dielectric film can be "healed" or rectified. Thus, a dielectric free film is possible.
When a pinhole defect occurs in the di-electric film, there is a short circuit between the electrode layers on both sides.
This results in a heavy current flowing at the point of the fault. this current causes a portion of the film layers to melt and vaporise. This breaks the connection between the film layers and fault.
The energy expended in reparing the fault is very small of the order of micro-watts. The process of self-healing is completed in about 10 microseconds.