Experiencing illness upon returning home from deployment or during holidays may indicate the immune system's response to a slight reduction in stress levels.

“um I tend to get sick at the end of the year last two years it was Christmas this year it was Thanksgiving and um you know bridg and I always joke about it it's because I slightly turn the engine down a little and then the you know the immune system yeah that's the way it works everyone thinks stress depletes the immune system and indeed it can yeah but if you think about it in evolutionary adaptive you know ways go go go go go allows you to saave off the infection or at least to not have the symptoms of combating infection and then when you relax a little bit go on vacation boom you get sick”