A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 6:1On Neginoth (See on Psa 4:1, title) upon Sheminith--the eighth--an instrument for the eighth key; or, more probably, the bass, as it is contrasted with Alamoth (the treble, Psa 46:1) in Ch1 15:20-21. In deep affliction the Psalmist appeals to God's mercy for relief from chastisement, which otherwise must destroy him, and thus disable him for God's service. Sure of a gracious answer, he triumphantly rebukes his foes. (Psa 6:1-10)
He owns his ill desert in begging a relief from chastisement.
psa 6:2I am weak--as a culled plant (Isa 24:4).
my bones--the very frame.
are vexed-- (Psa 2:5) --shaken with fear.
psa 6:3how long?--shall this be so (compare Psa 79:5).
thou--The sentence is incomplete as expressive of strong emotion.
psa 6:4Return--that is, to my relief; or, "turn," as now having His face averted.
for thy mercies' sake--to illustrate Thy mercy.
psa 6:5(Compare Psa 115:17-18; Isa 38:18). There is no incredulity as to a future state. The contrast is between this scene of life, and the grave or Sheol, the unseen world of the dead.
give . . . thanks--or, "praise for mercies."
psa 6:6By a strong figure the abundance as well as intensity of grief is depicted.
psa 6:7consumed--or, "has failed," denoting general debility (Psa 13:3; Psa 38:10).
waxeth old--or, "dim."
grief--mingled with indignation.
psa 6:8Assured of God's hearing, he suddenly defies his enemies by an address indicating that he no longer fears them.
psa 6:10and knows they will be disappointed and in their turn (compare Psa 6:3) be terror-stricken or confounded.