Disappear is about the feeling of slowly slipping away from the world, and from each other. The speaker begins with a quiet, uneasy thought: maybe everyone is sinking, down through the ground and toward the bottom of the ocean, the bottom of the world. The question "What is there to keep us here?" sits at the heart of it. Nothing seems to hold us in place. There are no anchors and no ropes, so people don't crash down so much as float into oblivion.
The mood is hazy, lonely and resigned. The speaker doesn't sound panicked, just tired and unsure, as if drifting is simply what happens. People try to find peace while they drift, which makes the poem feel almost gentle. Then the last two lines change the tone. A collision can "tear it all to pieces," suggesting that the fragile calm we find alone can be shattered when our lives crash into someone else's. The poem ends on that sense of fragility, with no comfort offered.