If you work beyond your capacity, you will naturally feel ......

If you work beyond your capacity, you will naturally feel tired.
In this context, "tired" is the most appropriate adjective to describe the feeling one would experience after working beyond their capacity. "Tired" means feeling a need for rest or sleep due to exertion or fatigue. Therefore, "tired" is the correct choice to complete the sentence, accurately conveying the expected outcome of working beyond one's capacity.