An Etymological Dictionary of the German Language/schwitzen
schwitzen, vb., ‘to sweat, perspire,’ from the equiv. MidHG. switzen, OHG. swizzen; Goth. *switjan is wanting. The Teut. root swī̆t, Aryan swī̆d, is primit. Aryan, as was observed under Schweiß (a common Aryan root for ‘to freeze’ is wanting; comp. Winter, Schnee, frieren, and Sommer); comp. Sans. svidyâ-mi, from the root svid, ‘to perspire,’ Gr. ίδίω, ‘I perspire,’ ἱδρώς, ‘perspiration,’ for σϝϊδ-, and further Lat. sûdare, ‘to perspire’ (for *swoidare), Lett. swidrs, ‘perspiration.’