hold your breath
hold (one's) breath
hold your ˈbreath
1 stop breathing for a short time, for example because you are afraid of something or very anxious about something: I held my breath as the car skidded towards me.
2 be anxious while you are waiting for something that you are worried about: ‘When will you hear about your job application?’ ‘Not till next week. I’m holding my breath until then.’
3 (informal) don’t hold your breath used for telling somebody that it’s not worth waiting for something: We’ll let you know if there’s any work for you, but don’t hold your breath.