I'm just flat on my ass. I need some rest.
•After the day of the marathon, Pete was flat on his ass for a week.
2. Fig. Inf. broke; financially destroyed. (Potentially offensive. Use only with discretion. An elaboration of flat broke.) •Sorry, I can't help you. I'm broke—flat on my ass.
•The guy's flat on his ass. Can you help him out with a loan?