Account for the poets choice of the expression, 'cease to be' (line 1) instead of the word 'die'. In the poem when I have fears that I may cease to be.

"Cease to be", is referring to the loss of consciousness and being that would come with death, whereas "die" is only body deep. So "cease to be" means the same as "die", but covers the mental and subconscious levels of being, as well as the physical.

It could also be seen as a shortening of the phrase "cease to be alive", if you wanted it to