From Longman Dictionary of Contemporary Englishbe (flat) on your backbe (flat) on your backa) to be lying on your back – used to emphasize that someone seems unlikely to get up soon He was drunk and flat on his back on the street. b) to be so ill that you cannot get out of bed Their best player was flat on his back in hospital. c) if a business, country, economy etc is on its back, it is not successful The UK market was flat on its back. → back
Examples from the Corpus
be (flat) on your back• He's been flat on his back in the hospital for a week.• His father was on his back night and day.• The sun was on his back as he swung himself over her and her long legs parted in expectation.• What else would he need if he were going to be flat on his back or stomach?• The child was on her back, unconscious.• The jelly cupboard was on its back, its contents lying in a heap in the corner of the bottom shelf.• After I was on its back, we all took off again on a run.• The result is that the liter pop bottle you tossed out six months ago may be on your back today.• Her eyes opened; she was on her back.be flat on your backbe flat on your backa) DOWNto be lying down so that all of your back is touching the floor b) ILLto be very ill so that you have to stay in bed for a period of time I’ve been flat on my back with the flu all week. → flatExamples from the Corpus
be flat on your back• Arthur was flat on his back under the car.• Babs said it was all very well but had he forgotten their leading man was flat on his back in Sefton General?• What else would he need if he were going to be flat on his back or stomach?• I've been flat on my back with the flu all week. 