context: You breathe without thinking because your body does it for you automatically. But things can change your breathing pattern and make you feel short of breath, anxious, or ready to faint. When this happens, it's called hyperventilation, or overbreathing. That's when you inhale much deeper and take much faster breaths than normal. This deep, quick breathing can change what's in your blood. Normally, you breathe in oxygen and breathe out carbon dioxide. But when you hyperventilate, the carbon dioxide levels in your bloodstream drop too low. You'll notice it right away because you'll start to feel sick. Hyperventilation happens most often to people 15 to 55 years old. It can come about when you feel nervous, anxious, or stressed. If you hyperventilate often, your doctor may tell you that you have hyperventilation syndrome. Women hyperventilate more often than men do. It may happen more often when a woman is pregnant, but the problem usually goes away on its own after the baby is born. Many conditions and situations can bring on hyperventilation, including: Anxiety disorder Panic attack Asthma Stress Worry or anxiety Hard exercise Emphysema or another lung disease Side effects from certain drugs High altitude Having a head injury Shock You may not always be aware that you're overbreathing. But signs may include: Shortness of breath, or feeling that you can't get enough air A faster than normal heartbeat Feeling faint, dizzy, or lightheaded Pain or tightness in your chest Frequent yawn or sighs A numb, tingly feeling in your hands or feet You may be able to stop yourself from hyperventilating if you focus on taking controlled breaths. These steps may not feel natural, but don't let that stop you. Controlled breathing may help you begin breathing normally once again. If it works, you should feel better again within half an hour. You can do it a couple of ways: Purse your lips. Put your lips into same position that you'd use to blow out birthday candles. Breathe in slowly through your nose, not your mouth. Then, breathe out slowly through the small opening between your lips. Take your time to exhale, and don't blow the air out with force. Repeat these steps until you feel normal. Limit your airflow. Keep your mouth closed, and press one nostril closed with your finger. Breathe in and out through the open nostril. Don't inhale or exhale too quickly, and don't exhale too hard. Repeat several times. You can switch nostrils if you like. Just do all your breathing through your nose, not your mouth. If you're with someone who's hyperventilating, encourage him try these moves. Make sure that he inhales and exhales slowly, and coach him to repeat as long as needed, since you won't see an instant change. If you aren't able to get your breathing under control within a few minutes, or if you're trying to change your breathing patterns and it isn't working, see a doctor or go to the emergency room right away, especially if you have any pain. Do the same for anyone else who's hyperventilating. If this isn't your first time hyperventilating and the problem gets in the way of your normal activities, you may have hyperventilation syndrome or an anxiety problem. Your doctor or therapist can find a diagnosis and help you manage the problem. Medication may help some people.