wait for the other shoe to drop

wait for the other shoe to drop {AmE} (to wait for something bad to happen; await a seemingly inevitable event) — ждать неизбежного, ждать самого страшного

Example 1:
Beth: Every time I've ever put myself out there, I've gotten hurt.
Every time. It's like I meet a guy, and I think it's great. And anyone else would just be thinking about how much greater it's going to get. And I'm constantly waiting for the other shoe to drop.
<...>
Nick: No other shoes are going to drop, Beth. This is real.
(Mv."When in Rome", 2010)

Example 2: Once a company starts laying of employees, those who are still working feel they are waiting for the other shoe to drop. (thefreedictionary.com)

Можно еще что-то вроде "известись от нетерпения". Или просто "напряженно ждать". (http://www.efl.ru/forum/threads/9767/)

Waiting for the other shoe to drop means that you're waiting for something bad to come along and spoil something that is "too good to be true."

This expression alludes to a person awakened by a neighbor who loudly dropped one shoe on the floor and is waiting for the second shoe to be dropped. (TAH)