Hamlet's monologue in the presence of Ophelia in Act III, Scene 1 is a meditation upon the state of existence in which he ponders if by dying a person can put to sleep "the thousand natural shocks/That flesh is heir to." For in sleeping, according to German philosopher Schopenhauer, death is not a total annihilation; there may yet be "dreams," memories of love etched forever in one's heart.
Further, as a Catholic, Hamlet is worried about the spiritual consequences of ending one's existence by committing suicide since suicide is a mortal sin that condemns one to hell and prohibits one from being buring in a consecrated cemetery. After all these reflections, Hamlet concludes,
Thus conscience does make cowards of us all,
and thus the native hue of resolution
Is sicklied o'er with the pale cast of thought,
And enterprises of great pitch and moment
With this regard their currents turn awry
And lose the name of action. (3.1.82-87)
The dilemma that one faces with death is that of the factor of the unknown that looms upon his consciousness and effects his fear of dying.