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Anxiety is the voice in the back of your head that says, “Something bad is going to happen.” It’s what keeps you awake at 2 a.m. thinking about something embarrassing you did five years ago.

Not all introverts have anxiety, and and ambiverts can struggle with it, too. To be clear, and anxiety aren’t the same thing. Introversion is a preference for calm, minimally stimulating environments, while anxiety is a general term for disorders that cause excessive , worrying, and nervousness. Still, for many introverts, anxiety is a regular part of their lives. And indeed, anxiety is more common among introverts than extroverts, according to Laurie Helgoe.

Sometimes anxiety is obvious (think: and sweaty palms), but that’s not always the case. Many people live with a form called “high-functioning anxiety.” Outwardly, they appear to have it all together. They may even lead very successful lives. No one can tell from the outside that they’re driven by fear. Sometimes they don’t even realize it themselves.

Although not an official diagnosis, high-functioning anxiety is something many people identify with. It’s closely related to , which affects 6.8 million adults in the U.S., with women twice as likely to experience it as men.

15 Signs of High-Functioning Anxiety

1. You’re always prepared.

Your mind frequently jumps to the worst-case scenario in any given situation. As a result, you may find yourself over-preparing. For example, you might pack underwear and makeup in both your checked luggage and your carry-on, just in case the airline loses your suitcase. People see you as being the reliable one — your preparations often do come in handy — but few people (if any) realize that your “ready for anything” mentality stems from anxiety.

2. You may be freaking out on the inside, but you’re stoic on the outside.

Interestingly, many people with high-functioning anxiety don’t reveal just how nervous they are, which is another reason why it’s often a secret anxiety. You may have learned to compartmentalize your emotions.

3. You see the world in a fundamentally different way.

Your anxiety isn’t just "in your head.” Researchers from the Weizmann Institute of Science in Israel found that people who are see the world differently than people who aren’t. In the study, anxious people were less able to distinguish between a safe stimulus and one that was earlier associated with a threat. In other words, anxious people overgeneralize emotional experiences — even if they aren’t threatening.

4. You constantly feel the need to be doing something.

This can be a real problem if you’re an introvert who needs plenty of downtime to recharge. This doesn’t necessarily mean you’re attending lots of social events; instead, you may feel a compulsion to always be getting things done or staying on top of things. Staying busy distracts you from your anxiety and gives you a sense of control.

5. You’re outwardly successful.

Achievement-oriented, organized, detail-oriented, and proactive in planning ahead for all possibilities, you may be the picture of success. The problem is, it’s never enough. You always feel like you should be doing more.

6. You’re afraid of disappointing others.

You might be a people-pleaser. You’re so afraid of letting others down that you work hard to make everyone around you happy — even if it means sacrificing your own needs.

7. You chatter nervously.

Even though you’re an introvert who prefers calm and quiet, you chatter on and on — out of nervousness. For this reason, you're sometimes mistaken for an extrovert.

8. You’ve built your life around avoidance.

You’ve shrunk your world to prevent overwhelm. You stick to routines and familiar experiences that give you a sense of comfort and control; you avoid intense emotional experiences, like travel, social events, conflict, or anything else that might trigger your anxiety.

9. You’re prone to rumination and overthinking.

You do a lot of negative . You often replay past mistakes in your mind, dwell on scary “what if” scenarios, and struggle to enjoy the moment because you’re expecting the worst. Sometimes your mind races and you can’t stop it.

10. You’re a .

You try to calm your worries by getting your work or your appearance just right. This can bring positive results, but it comes at a cost. You may have an “all-or-nothing” mentality (“If I’m not the best student, then I’m the worst”). You may have unrealistic expectations of yourself, and a catastrophic fear of falling short of them.

11. You have aches, repetitive habits, or tics.

According to psychotherapist Annie Wright, your anxiety might manifest physically in your body as frequent muscle tension or aches. Similarly, you might unconsciously pick at the skin around your nails, tap your foot, scratch your scalp, or do other repetitive things that get your nervous energy out — even if you appear composed in other ways.

12. You’re tired all the time.

Your mind is always going, so you have trouble falling asleep or staying asleep. Even when you sleep well, you feel tired during the day because dealing with a constant underlying level of anxiety is exhausting.

13. You startle easily.

That’s because your is in overdrive. A slammed door, an ambulance siren, or other unexpected sounds really rattle you.

14. You get irritated and easily.

You’re living with constant low-level stress, so even minor problems or annoyances have the power to frazzle you.

15. You can’t “just stop it.”

Anxiety isn’t something you can tell yourself to just stop doing. In fact, the researchers from the Weizmann Institute of Science found that people who are anxious have somewhat different brains than people who aren’t. They noted that people can’t control their anxious reactions, due to a fundamental brain difference. (However, you can learn to cope with your anxiety and greatly lessen it.)