Yes we can know if we have been hacked. If my wife rather look at her FB and all the things her "friends" post, but has no time to talk to me, and look at my eyes, her brain was hacked. If your friend which you are having lunch with is looking at FB rather than enjoying the atmosphere of the restaurant, the artistic arrangement of the dish, the decor, architecture, the background music. etc...FB and all other Centralized platforms have hacked your friends brain.