Sense is a tiny poem about what happens to a person when they are close to someone they love, or at least someone who overwhelms them. The first two lines describe silence and darkness, and both seem to do damage: the silence makes the speaker feel deaf, the darkness makes them feel blind. Hearing and sight are being switched off, not just quieted or dimmed.
Then the third line turns the poem around. The cause is "being with you." The emptiness of the first lines is tied to the other person, which suggests a feeling of confusion or of being swallowed up by them.
The final line plays on the word "sense." It can mean the physical senses just described, but also good judgment, as in common sense. The speaker is losing both at once. Note that the poem spells "loosing" where "losing" is meant, but the meaning is still clear.
The mood is dizzy and intense, with a hint of helplessness. It could be read as being swept away by love, or as being unsettled by a relationship. The poem leaves that open.