Complex sentence: On Christmas Eve Čiurlionis fell into a profound depression and at the beginning of 1910 was hospitalized in a sanatorium in Pustelnik, in Marki, northeast of Warsaw.
Split into simpler sentences: On Christmas Eve Čiurlionis fell into a profound depression there. In the beginning of 1910 he was hospitalized in a sanatorium in Pustelnik in Marki, northeast of Warsaw.