I agree too lilian. "se va" sounds better.
But I see "M. va a dormire".
I wanted to remain close to the original form of the sentence, without adding new words.
If it was "M. se ne va a dormire", I would translate "M. se va a dormir".
However I think the meaning and the rightness of the sentence don't change.
Hola meridi, a veces tenemos que cambiar un poco las expresiones para que en el idioma alvo suenen naturales. Aunque no sea textual, en español se dirÃa "se va a dormir" es una acción que llama al reflexivo (irse, levantarse, etc)
I found many sentences and spanish texts with both of situations "ir" and "irse".
But you are a spanish expert, so I'll follow your suggestion
Just tell me if I have to change the translation, or you'll do it.