Anxiety is something I have been dealing with my entire life, as have many people across the globe.
People that don't experience anxiety usually just associate the word with somebody being nervous. Their response to somebody being anxious is, "Oh, just calm down." That's exactly what not to say to somebody with anxiety. It's not just something people feel. Generalized anxiety is a mental disorder.
Most general anxiety disorders have to do with the imbalance of chemicals in one's brain, including serotonin and dopamine. Much like depression, it can't really be turned off and affects the same areas in the brain. It is something physical and not made up, even though many people claim it is.
Having dealt with anxiety my entire life, I've realized it's really hard to communicate what you're feeling while having anxiety or anxiety attacks. Mine come in the form of terrible stomachaches and being irrational, although symptoms could range from insomnia to irritability.
Anxiety is different for everybody. If one day I wake up feeling anxious, it's usually from a small trigger that grows. I can't stop it. Anxiety is an abstract mental problem that is often just blown off. People with anxiety are less likely to get help for it, because society has talked about anxiety in such a light manner. It took me years to figure out what was going on with me, and when I did, I wasn't sure what to do about it or how to fix it. We talk about depression all the time in media, but anxiety problems don't get much light.
Nervousness is something that comes naturally in humans. Everybody at some point in their lives feels nervous. Anxiety is nervousness, but increased by a thousand (at least for me). The human brain blows things out of proportion and makes being nervous so much harder to deal with. It wasn't until this last August that I found something that very obviously helped me with how I dealt with my anxiety. After going to my doctor, he prescribed me an anti-anxiety medication. It's funny because the medicine I'm on is also used to help with depression, as they are very similar in nature.
Honestly, I'm not mad that people don't go out of their way to learn about what anxiety is, but it is something that you may see in your day to day life. Anxiety is always different. My anxiety has affected me through every decision I make.