The time dependence of the photoluminescence of GaN/AlN quantum dots (QD's) after high photoexcitation is examined on a large time scale. A continuous change in energy peak is reported, resulting in a giant energy shift of more than 1 eV after delays of several hundreds of microseconds. Simultaneously, the intensity decreases over more than seven orders of magnitude with a complex dynamics. These results are explained by the screening of the internal electric field due to the accumulation of electron-hole pairs in the dots. The dynamics can be qualitatively described by considering the change of the squared overlap integral and the effect of the number of the electron-hole pairs in the QD itself on the radiative lifetime.