1. as much as possible
working/running flat out
Flat out is a phrase that can refer to lying down stretched out particularly if you are exhausted. Flat out can also mean 'completely' or 'without hesitation' and is a phrase that is used for emphasis, for example, 'I flat out refused to cook for him'. To be flat out can also mean to be extremely busy.
flat out asleep/on the bed
To be flat out can mean to be sleeping stretched out somewhere usually because of exhaustion or extreme tiredness.