The only 2 songs I could think of, Pumped Up Kicks, and 99 Luftballons/99 Red Balloons were already brought up. So I had to think of some different songs. And I can't. Looked through a bunch of songs on my phone and back of some of my CD cases and I can't think of any right now.

Closest I can think of was just a video of someone reacting to the Japanese vocaloid song 「ごめんね ごめんね」 ( I'm sorry I'm sorry )by Kikuo and not knowing what the song meant until looking up the lyrics. Even then, that's not a very upbeat song.

Edit:

I thought about "Belong" by R.E.M., but I would say it's near upbeat but not quite there. Also, the lyrics are more cryptic and confusing to dissect than depressing in my opinion.

Edit 2:

Wouldn't say it's quite upbeat either, but Mighty K.C. from For Squirrels as well. Not quite upbeat but definitely depressing lyrics considering it's about death.