Not so much "upbeat" as "relaxing", but there's the theme to the film,
M.A.S.H.:
"Suicide is Painless", the lyrics to which are about what you'd expect from a song of that title.
https://www.youtube.com/watch?v=whhAg6bA3_o&rco=1
Needless to say, the TV series just used the instrumental version in its intro, and even accounting for the lyrics' removal, the tune is more upbeat there:
https://www.youtube.com/watch?v=LJuJNw6oayg
The
other
instrumental version for the TV series, used in the closing credits, was
even more
upbeat:
https://www.youtube.com/watch?v=AWp7N3L1klM