At the other end of the spectrum, here's a 1967 story by Harlan Ellison about how eternal life could really, really suck

AM has altered me for his own peace of mind, I suppose. He doesn't want me to run at full speed into a computer bank and smash my skull. Or hold my breath till I faint. Or cut my throat on a rusted sheet of metal...I have no mouth. And I must scream. 

I Have No Mouth, and I Must Scream