lassitude: n. weariness of body or mind from strain, oppressive climate, etc.; 
lack of energy; listlessness; languor.

He exhaled harshly as the second boot also landed on top of the rock, because unlike the first, it had slipped against a protrusion on the uneven surface and twisted the ankle inside. 

Making a decision, Hyukjae decided to ignore the injury and finish the last quarter of the twenty mile tramp while fighting lassitude and pain. 

As a leader, he didn't want to hinder the group's progress and set a bad example.

As a son, brother, and boyfriend, he felt guilty for not looking after himself properly and pretending that he was strong enough.

It was becoming a habit.