A quick survey of English translations of Psalm 4:4 shows that there is little agreement about how ragaz should be rendered:
NIV In your anger do not sin; when you are on your beds, search your hearts and be silent. Selah
NASB Tremble, and do not sin; Meditate in your heart upon your bed, and be still. Selah.
BBE Let there be fear in your hearts, and do no sin; have bitter feelings on your bed, but make no sound. (Selah.)
NRSV When you are disturbed, do not sin; ponder it on your beds, and be silent. Selah
NKJV Be angry, and do not sin. Meditate within your heart on your bed, and be still. Selah
The definition given by Strong's seems to support all of these senses. Perhaps the ambiguity was intentional on the part of the Psalmist. But it seems odd that some translations treat the word as a command ("Be angry") and others as a condition ("In your anger"). How does the Hebrew grammar work here?