An Etymological Dictionary of the German Language/Schlummern
Schlummern, vb., ‘to slumber,’ from the equiv. late MidHG. (MidG.) slummeren, slumen; comp. Du. sluimeren; AS. slûmerian, E. to slumber, AS. slûma, Northern E. sloom, ‘to slumber.’ The root (Alem. šlûne, šlûre, ‘to slumber’) contained in these words appears in Goth. slawan (slawaida), ‘to be silent,’ in a curious divergent meaning, to which MidHG. slûr, m., ‘idling, idler’ (comp. Schlaraffe), is also allied. The prim. idea of the whole group is ‘to be quiet, inactive.’