Shakespeare: Macbeth doubts?

For lines 91-92 - this is a metaphor comparing the wine and a wine cask to life. Wine is like the blood or vitality of life... Lees is defined as the sediment left over in the cask. Macbeth is saying he might as well be dead - that it would be easier if he died. Because life -- or the wine of life -- is gone now that he has committed these deeds, and all that is left is the like, memory of life. He is like living dead.