What's the difference between "deadly" and" completely",please ?

For instance :
The detective had been up all night looking for clues, and now he was deadly/completely tired.

Thank you very much for reading my question.

Question

What's the difference between "deadly" and" completely",please ?

For instance :
The detective had been up all night looking for clues, and now he was deadly/completely tired.

Thank you very much for reading my question.

Answer

He is so tired he feels like he is dead. You could also say deathly tired. It only means completely in this or a similar sense.

Answer

Deadly tired would not be grammatically correct. Deadly means something that is very dangerous and could cause death. Completly is when something is totally complete. Eg completely finished putting all the toys back in the box.