Death March to the Parallel World Rhapsody

 Death March kara Hajimaru Isekai Kyusoukyoku is an ongoing web novel series by Hiro Ainano. When computer programmer Ichiru "Satou" Suzuki takes a nap under his desk at the end of a thirty hour workday, he dreams about the games he's spent the day debugging. Or so he thinks.

For the light novel version, and it's subsequent adaptations, see Death March To A Parallel World Rhapsody.