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

sink into sth

phrasal verb with sink us uk /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)