angry

St. Paul, in Ephesians 4, gives this classic advice on anger:

"In your anger, do not sin. do not let the sun go down while you are still angry."

Paul is quoting Psalm 4.4. However, your Bible will probably not render Ps 4.4 that way. That's because Paul was using a different version of the Old Testament; namely, the Septuagint--a Greek translation of the Hebrew Bible. The Septuagint does talk about 'anger.'
But check virtually all modern English translations of Ps 4.4 and you will get something like: "Tremble and do not sin; when you are on your beds, search your hearts and be silent" (TNIV). David is telling his enemies to tremble because of their disobedience to God and stop telling their lies.
Paul, using the Septuagint, applies Ps 4.4 to anger. He doesn't say it is sinful to be angry (though other parts of Scripture condemn self-righteous anger); but he advises that it is best to deal with our anger quickly rather than let it fester. We are tempted to sweep our angry feelings under the rug and not rock the boat. But angry feelings unexpressed (or better, unreported) do not go away; they become poison. Don't let that happen, says Paul. Deal with it now. Report your feelings. Tell someone. Talk it out.

At the end of Psalm 4, David says, "In peace I will lie down and sleep, for you alone, Lord, make me dwell in safety." We sleep better if we are honest with each other, and unpack our feelings during the day.