Well, you are correct in translating テストに失敗して (tesuto ni shippoi shite) as "I failed a/the test". As I understand it, 撃沈 is a metaphorical expression used to show that you are disappointed in yourself over something that didn't turn out as you had wished it would have. Is that correct? If so, then I think there are a number of ways you could indicate that in American English. For instance, 1. I failed a/the test. EPIC FAIL! 2. I failed a/the test. Darn it! / WTF?!? 3. I failed a/the test. *Hides (his) head in shame* 4. I failed a/the test. Ugh. I thought I was going to do better on it! 5. I failed a/the test. So disappointed. / I'm so disappointed. 6. I failed a/the test. Ugh! #1 you will see in Facebook posts. #2 is swearing and very vulgar so you should not use this in a formal context or around anyone who isn't a really close friend. Hehehe. #3 uses a chat action. We place a verb in the 3rd person singular form with no subject between two * characters to indicate the action. In this case, it stands for "I am hiding my head in shame." but you are speaking of yourself in the 3rd person singular. I have actually heard people say these actions in person too, which sounds as strange and funny as hearing "LOL" in person. Hehehehe. In #5, you can say "so disappointed" instead of "I'm so disappointed" when posting on Facebook. Often times in informal language and on Facebook, we drop the subject of the sentence and write like this. In #6, "ugh" is a sound we make to indicate disappointment or annoyance over something.

Are you saying two actions "(1) The test was bad, therefore (2) I did something" ? Or are you saying simply "I did badly in the test" ? For the latter, we might say "I really blew that test." We would not say "I sunk that test" because it would be ambiguous. It could have a negative interpretation, like a ship sinking, or a positive interpretation, like sinking a golf ball in the hole.