The body's first reaction to a stressor, in the is a temporary state of shock during which resistance to illness and stress falls below normal limits.

Answer;
Alarm stage
The body's first reaction to a stressor, in the alarm stage, is a temporary state of shock during which resistance to illness and stress falls below normal limits.

Explanation; 
 Alarm stage is the first stage in the general adaptation syndrome; others are the resistance stage and the exhaustion stage;
During the alarm stage; The body's first reaction to a stressor is a temporary state of shock during which resistance to illness and stress falls below normal limits. In an attempt to code, the body releases hormones that, in a short time, adversely affect the functioning of the immune system. During this time the body is susceptible to infections from illness or injury.

Bc they get tired from playing with other kittens