"Sea Fever" is an excellent title for this poem because it refers to the way that for some people the desire to see the sea and be close to it and sail upon it can act in the same way as a fever, which cannot be shaken off. Note how the all-consuming desire of the speaker dominates the poem, with each stanza beginning with the same phrase:
I must go down to the seas again...
The repetition emphasises the way that this desire dominates the speaker and he is unable to think of little else except for the sea and how it sounds, feels, looks, tastes and what is associated with it. If you think of other kind of "fevers" that we can get, we can be in a "fever" for love, when all we do is think of the object of our affection, or we can be in a "fever" for a particular sport when an important match is being played. It is this kind of single-minded focus to the exclusion of everything else that is captured in the title of "Sea Fever."