"Low tide" is a tiny poem that sounds like a restless body in bed at night. The speaker pictures themselves as an "oyster out of water," exposed and out of place, like a creature left behind when the sea pulls away. Nothing is going right: they "poke all about," feeling around without finding comfort or rest.
The bed seems to be the real setting. The phrase "rest-vexed bed" suggests sleeplessness, a bed that torments instead of soothing. The speaker also calls themselves a "little thief," which hints at guilt or a sense of taking something they shouldn't, though the poem doesn't say what. Judging by "together with," there may be another person or presence lying close by, but that is only an inference.
The mood is uneasy, cramped, and a little self-mocking. The clipped lines and the sound play in "low way to lay" make the poem feel like muttering in the dark, half-awake and slightly ashamed.