I think this is the original recording. My transcription from the Internet Archive:


GOING DOWN SLOW
(Jimmy Oden)
As recorded by St. Louis Jimmy [Oden] on Bluebird B-8889-B, 1941.

I have had my fun, if I don’t get well no mo’. (2x)
My health is failin’ me, an’ I’m goin’ down slow.

Please write my mother; tell her the shape I’m in. (2x)
Tell her to pray for me; forgive me of my sin.

Tell her: don’t send no doctor; doctor can’t do no good. (2x)
It’s all my fault; didn’t do the things I should.

On the next train south, look for my clothes home. (2x)
If you don’t see my body, all you can do is moan.

Mother, please don’t worry; this is all in my prayer. (2x)
Just say your son is gone out of this world somewhere.

- - -
The Internet Archive also has recordings by:
Billy Wright and Orchestra, Savoy 870-A, 1952.
St. Louis Jimmy, Parrot 83, 1956.
Brownie McGhee, Alert 405-A, no date.

Spotify also has recordings by:
Champion Jack Dupree, on “Blues from the Gutter,” 1958.
Howlin’ Wolf, on “Howlin’ Wolf,” 1962.
Aretha Franklin, on “Aretha Franklin Arrives,” 1967.
Canned Heat, on “Canned Heat,” 1967.
Bobby “Blue” Bland, on “His California Album,” 1973.
Ray Charles, on “Ray Charles Volume II,” 1974.
Duane Allman, on “Dreams,” 1989.
B. B. King, on “The Best of B.B. King,” 1991.
Eric Clapton, on “Pilgrim,” 1998.
Peter Frampton Band, on “All Blues,” 2019.
(Tom Waits has a different song by the same title.)