Bone tired

Exhausted to the very core; tired in a deep, fundamental way that seems to penetrate to one's bones. Profoundly weary.

This phrase appeared in the 19th century, using bones as a metaphor for the deepest, most essential part of the body. Since bones are the structural foundation of the body, being 'bone tired' suggests exhaustion that goes beyond surface fatigue to the very framework of one's being.