The onset of forbidden line emission in the spectrum of a proto-planetary nebula has been detected for the first time in the lapse of only two years. IRAS 06562-0337 was first observed in December 1987 and October 1988, showing only the Balmer lines in emission. A third spectrum obtained in February 1990 shows a quite different appearance, with forbidden emission lines typical of a low excitation planetary nebula. The effective temperature of the central star has clearly increased over these two years. Another spectrum obtained in March 1992 however, shows that the forbidden lines have disappeared. This, combined with the nature of the H-alpha profiles at different times, reveals the episodic nature of the mass loss mechanism which most likely precedes the formation of a planetary nebula.