When I say, my bed shall comfort me
When he thought within himself that he would lie down upon his bed and try if he could get a little sleep, which might comfort and refresh him, and which he promised himself he should obtain by this means, as he had formerly had an experience of:
my couch shall ease my complaint;
he concluded, that by lying down upon his couch, and falling asleep, it would give some ease of body and mind; that his body would, at least, for some time be free from pain, and his mind composed, and should cease from complaining for a while; which interval would be a relief to him, and of considerable service. Some render it, "my couch shall burn" F8; be all on fire, and torture me instead of giving ease; and so may have respect to his burning ulcers.
F8 (avy) "ardebit", Pagninus; so Kimchi in Sepher Shorash. & Ben Melech in loc.