Charles Ellicott Commentary Psalms 149:5

"Let the saints exult in glory: Let them sing for joy upon their beds." — Psalms 149:5 (ASV)

The two clauses are directly parallel:

“Let the chasîdîm raise a cry in glory:
Let them sing aloud upon their couches.”

Either the rejoicing is carried far into the night, and when retired to rest the happy people burst out anew into singing; or , the couches may rather be the divans where feasts were held.