Sinking or submersion (e.g., a ship foundering); going down beneath the surface. Can be used metaphorically (e.g., a business failing).
夜中の嵐で船が沈没した。
The ship sank during the storm at night.
沈没事故で多くの乗組員が救助された。
Many crew members were rescued in the sinking accident.
会社が資金不足で沈没寸前だ。
The company is on the verge of collapse due to lack of funds.
Colloquial: being extremely drunk; getting dead drunk.
昨夜は飲みすぎて沈没した。
I drank too much last night and got completely wasted.
彼は飲み会で沈没して終電を逃した。
He got totally drunk at the drinking party and missed the last train.
Colloquial: indulging in pleasures to the point of neglecting work or duties (often implies excessive nightlife activity).
彼は最近沈没して、平日に出社しないことが多い。
Lately he's been slacking off and often doesn't show up at work on weekdays.
あの先輩は夜の街に沈没して、しょっちゅう遅刻する。
That senior gets lost in the nightlife and is frequently late.
Slang (backpacker): staying in one place for a long time during travel; settling in a spot instead of moving on.
彼はバリで沈没して半年以上動いていないらしい。
Apparently he settled in Bali and hasn't moved for over six months.