go under

verb6

1. •
   To descend into a body of water; to founder.

   • The boat was too heavy and went under.
2. •
   To collapse or fail, e.g. by going bankrupt.

   • In the crisis, the company was forced to reduce its costs in order to avoid going under.
3. •
   To be named; to call oneself.

   • He goes under the name of Mr X to remain anonymous.
4. •
   To enter a trance, state of hypnosis, etc.

   • "But I went under nicely and I am glad there were some fine materializations." — 1925
5. •
   To die.

   • If we don't get him to a doctor, he'll go under for sure.
6. •
   (Australia, slang) To be imprisoned.