How's ちゃわなきゃ working in this sentence?

Question

I have a question about the usage of ちゃわなきゃ with 寝る in the following sentence, 先週みたいに途中に寝ちゃわなきゃいいけど。

I believe that the ちゃ is for things that must not be done, but I have no clue what わなきゃ is doing here.

I think the speaker is trying to tell the person she is talking to that he must not fall asleep in the middle of the activity like he did last week. I'm not quite sure what the いいけど may mean here either. I think it is separate from ちゃわなきゃ but I'm not sure what purpose it serves if someone MUST do something. Literally, it means good but... .

Anyways, if anyone could help me out, I'd appreciate it. I feel that there may be a level of slang here that I cannot grasp.

Answer 1

寝ちゃわなきゃ is a very contracted form.

Starting from the fully expanded version, this developed roughly as:

• 寝【ね】てしまわなければ
• 寝【ね】ちまわなければ
• 寝【ね】ちゃわなけりゃ
• 寝【ね】ちゃわなきゃ

I presume you understand the ～なければ + いい construction, so I won't explain that here.

In response to your comment. :)

～なければ is what you get from ない + conditional ～ば, and it means "if ～ isn't the case / if ～ doesn't happen". So ～なければ + いい means "it's good if ～ isn't the case / if ～ doesn't happen". When you're talking to a person, this can sometimes be translated as "you shouldn't do ～".