There currently is one option to travel by night train from Lublin (Poland) to Szczecin (Poland), taking between approximately 9 and 11 hours: Namely the IC 440. These lines are operated by PKP Intercity and Deutsche Bahn.
PKP Intercity, Poland's national long-distance operator, connects cities across Poland and beyond its borders.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night.
In these night trains, there are only first and second class seats. The lights stay on all the time and there is no way to recline the seats.