Green’s Dictionary of Slang

conk (out) v.

also konk (out)
[conk v.2 ]

1. [1910s+] usu. of machinery, to collapse, to break down, to malfunction; thus conked (out) adj.

2. [1920s+] to lose consciousness.

3. [1940s+] to give up.

4. [1930s+] to die; thus conked, dead.

5. [1940s+] to fall asleep.

6. [1940s+] to knock someone out.