Depending on software, but typically major release is followed by a long list of bug reports, so you don't have time to be depressed. Software I wrote in my car

Depending on software, but typically major release is followed by a long list of bug reports, so you don't have time to be depressed. Software I wrote in my career is long-lived, so you never actually finish it. Could be different if it's something like a game that's published on specific date, but even that is now patched after release and often requires further work. Not much software nowadays is really finished not to be touched again. That said, I noticed this "down" effect earlier in life after completing something challenging, like passing a hard exam, etc. But not with software. If anything, we should stop sometime to reflect on what we achieved after longer period of time, it's too easy to be on a treadmill and never feel that anything significant is finished and accomplished.