For the big gloom to work well, it is best if it is truly bleak and overwhelming for the hero. It doesn’t have to be depressing, but that can factor into the moment, too. It can last for as short a period as a single line of dialogue, or it can be a single lyric line of a song, or an entire song. Or it can last for the better part of a scene or more. Any way you write it, the audience ought to sense that the hero has no way of recovering from his current state.
