Anxiety is usually in capital letters in the heads of people who deal with it. It's blocky, bold, and baleful. In short, it's everything that will not be ignored or managed through common sense and reason. Common sense says, "you can trust your friends," reason points out that the reason you do is because they have proven trustworthy, and then anxiety comes along and sticks a sneaky knife in your back: "if they don't betray you outright, what if they forget about you? What if they drop the friendship because it is no longer convenient to them?"
Anxiety is unreasonable, and for those who have dealt with the chronic version of it, a formidable enemy. It's one of those intangible mental and emotional things that the rest of world labels as worry, which is somewhat correct, only it's much bigger than the occasional worry. Instead of being something you identify: "I'm worried my car is going to be an expensive repair," it becomes a general dread and unease about life.
"Something is wrong and I can't identify it."