Is negative pressure bad and how to fix?
Many homes have only one main return located at the air handler. The separate rooms have a supply but the return is the space/gap under the room door. While closing a room door might not affect cooling too much, a hallway door cutting off a number of bedrooms would have a major effect. Installing a through vent above the hallway door might be the answer.
I love whole house fans but you have to cover them up in the attic during AC season because the vent that comes with them is not insulated and any negative pressure will suck hot air out of the attic.