deficiency or not

Recently, one of my ladies, fan leaves starting from the bottom turning a pale yellow ( it actually slowly takes over the leaf) and eventually the leaf just kindof comes right off the plant like its not attached anymore, while at the same time the upper leaves tips became brown and crispy to the touch. I know generally this means nitrogen defeciency, but I dont think thats the issue because it recently received a decent amount. Any idea what this combination might mean?? could this have any connection to a recent fungus gnat infestation thats now under control??