WM,The words of wisdom by SC say it all so please try not to Google. You posted, " I hate that these days everyone is on vacation and I can't stop thinking about it."
Are you anxious because everyone is on vacation? Could that be what is making you feel ill?
Are you on vacation too? Do you have plans or can you make plans to do something fun if your on vacation?
I know I ask lots of questions but sometimes we look so hard for a serious reason for why we feel the way we do and it is as easy as your feeling lonely with others all on vacation and having a good time.
Kindly,
Kitt