'At sea' or 'all at sea' - both are correct. An idiomatic expression to show that a person is lost, confused or doesn't know where to turn next.

'Hung' or 'Hanged' ? In the days when hanging was a legal execution method, a person 'will be hanged' or 'was hanged'. The process of 'hanging' someone involved purpose-built gallows. While the tense should technically never change, if a person hangs himself from a light fitting, a tree, or any other non purpose-built structure, then it's perfectly acceptable to say 'He hung himself'.
English, like any other language, evolves. These days, when hanging is no longer used as an execution method in Western countries, people are no longer 'hanged'. Therefore I feel it's almost natural that the correct past-tense of the verb 'to hang' (SOMETHING) is used.

By the way, isn't it interesting that even when the original subject is that of a student having his throat slit in a classroom full of kids, dying in a pool of blood on the classroom floor while his classmates screamed in terror unable to do anything to help, that the discussion has sunken once again into the depravity of criticising other posters' misplaced commas?

Certain posters here should be ashamed of themselves.

There are moments when foreign teachers are 'at sea' during their time in China, lost in the unique cultural response to powerful tragic events.

Don't copy other posters they may have missed out a word. It's 'all at sea' and nothing less hahaha!

Unless an FT has boarded a ferry that sails between Hainan and Xiamen, for example. Then he would be in Chinese territorial waters, which are part of China! But he posted 'at sea' rather than at sea!

So, 'all at sea' is correct. You are right.