when supressing estrogen during a cycle we use SERMS. WHen you come off your cycle you most likely do not keep running your SERMS unless you have issues with estrogen. What might happen when coming directly off from using something that supresses estrogen or inhibits it from binding. Estrogen will have a rebound effect where it bounces back to more then normal due to the supressed nature it was during your cycle and PCT. (Don't you wish your natty test levels would do this?)
Thats why it is usually recommended to taper your dosages of Nolva, arimidex, ect...during PCT.
I hope that kind of helped?