I wouldn’t call it hiding my feelings, I call it a choice, to determine whether or not something is worth addressing.
If I am in a less than high energy state I usually decline invitations so I do not have to pretend or hide my feelings. If it is a matter if someone violating my boundaries or behaving like a jackass I will address it in a timely and non-defensive way.
I have found that if something is on my mind or really bothering me for more than a day or two that is a signal to speak up, to thine own self be true.
My days of building resentments and then kitchen sinking another are long gone.
Speak up, change the situation or leave. Anything else is insanity.