We report a global decrease of the energetic neutral atom (ENA) flux coming from the entire nightside magnetosphere detectable out to dipole L = 14 during the growth phase of a substorm at 08:00--09:09 UT on 4 October 2000. The ENA images were obtained in the 27--60 keV range by the high energy neutral atom (HENA) imager onboard the IMAGE spacecraft. The underlying proton distribution is derived by inverting the ENA images using a constrained linear inversion technique. The magnetosphere experienced enhanced convection and the geomagnetic field at geosynchronous was stretched. The global ENA flux decrease is found to be related to the rapid stretching of the tail inducing a dusk to dawn electric field. The phenomenon can be explained either as a resulting choking of the E ¿ B drift from the tail, or, as an adiabatic de-energization of the azimuthally drifting ring current protons.