While "I Am" sometimes seems all about life and existence ("I am […] I am […] I am"), it's also super-obsessed with death. Setting aside the fact that the speaker yearns for death in the last stanza, there's all that stuff about how the speaker lives surrounded by a metaphorical shipwreck where there is no "sense of life." In fact, part of the reason the speaker wants to die is because everything around is metaphorically dead (friends are "gone," sounds are just "noise"). This is a very grave poem. On the bright side, we made a pun! (Grave as in serious, grave as in graveyard—get it? Huh? Yeah!)
Don't fret. The speaker reminds us that death isn't such a bad thing. It's like sleeping like a baby.
The speaker is both alive and dead. His body and mind are still "there" but he's like a ghostly, "vapor" as well. Spooky.