1. as much as possible
Professional
Social
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.
2. asleep
Professional
Social
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.