The music is actually taylored to the gameplay. The intensive part from 1:21-1:45 is when the screen fills to the brim with enemies and then at the last second you are able to survive the onslaught by quickly snatching a shortlived invicibility pick up.
Level 7 in Demonstar Secret Missions 1 is also taylored to fit the level. There are at least 1000 enemys flying at you during the last minute of the level and horror music is played.
