Going quiet to cool off is fine. Just say so. “I need ten minutes” beats disappearing.

Needing to cool off is reasonable; vanishing while you do it is not. From outside there is no difference between taking space and walking out, so the other person spends the whole interval guessing which one is happening. One sentence turns the first into something they can wait through.

Name the pause and the length: ten minutes, or after dinner. Then come back when you said you would, because that is what makes the next pause believable. If ten minutes becomes an hour, send one line saying so.