Meaning of “sink into sth” - Learner’s Dictionary

sink into sth

phrasal verb with sink uk us /sɪŋk/ verb (past tense and past participle sank, also US sunk, past participle sunk)

to slowly move into a sitting or lying position, in a relaxed or tired way:

I just want to go home and sink into a hot bath.

(Definition of “sink into sth” from the Cambridge Learner’s Dictionary © Cambridge University Press)