I would say feelings of worthlessness. You can't really see it on their body, but they can tell you if they choose to, so that makes it hidden in my opinion.
I hope that helps!
Stress is inevitable part of life so one should be able to manage it to be able to stay healthy. General Adaptation Syndrome has 3 stages that can help one understand the different stages the body undergoes when in stress. There is the Alarm Reaction stage which is the fight and flight, the Resistance stage in which symptoms like Irritability leading to fatigue and the Exhaustion stage which includes anxiety and depression
