wallow in

to indulge in an excessive way in feelings of self-pity (figurative meaning)

sich im Schlamm wälzen

to lie and roll around in mud, often for pleasure (literal meaning)

im Schlamm liegen und sich wälzen, oft zum Vergnügen (wörtliche Bedeutung)

to indulge in an excessive way in feelings of nostalgia (figurative meaning)