I can be dying inside while going through the motions of the day. It’s not difficult for me to know how others expect me to act. Acting fine is a cognitive process. You can probably mention right now how an emotionally stable or “mentally sane” person is supposed to act. It really is simple. A generally accepted lifestyle is one where a person wakes up every day, looks presentable, takes care of stuff that needs to be taken care of, eats and goes to sleep. This can sometimes be done regardless of how you feel inside. To say it’s difficult is an understatement, but it’s not impossible.