'Couches' in Psalm 149:5?

"Let the faithful exult in glory; let them sing for joy on their couches." (Ps. 149:5, NRSV)

Psalm 149,5: 'they shout with joy on their couches'
Th. Booij
Biblica, Vol. 89 (2008) 104-108. PDF

... In that verse, the element על־משכבותם, ‘on their couches’, is problematic.

Abstract
Ps 149,5 can be understood from the literary motif of intensified spiritual activity and receptivity in resting time, particularly in the night. Formally, the statement of this verse is related to Cant 3,1. In vv. 5-9 the psalm describes the feelings and mental images of YHWH’s faithful with regard to a future judgement on the nations. The consciousness of Israel’s special position, expressed in the preceding hallelujah-psalms as well, is brought to a climax.

continued...(pdf)