It’s metaphorical. He’s talking about falling as in his mood getting much worse. Or his life situation. And he’s implying his mood is already so low, it can’t get any worse. Poor guy.

In "there's nowhere left to fall," it means there’s no further "down" to go—they've already hit rock bottom, or the lowest emotional point. The phrase suggests a feeling of finality: there's nothing left to lose or risk, so it’s a make-or-break moment ("now or never"). It doesn't mean "nothing will fall"; rather, it emphasizes they've reached the lowest point possible.