4-7-8 breathing is a technique for deep relaxation. Many use this counting technique to manage stress and anxiety through controlled breathing. Specifically, it involves inhaling for the count of four, holding your breath for the count of seven, and exhaling for the count of eight.

The 4-7-8 breathing technique is based on the pranayama breathing exercise that is practiced during yoga for relaxation.

Using the 4-7-8 breathing technique activates your parasympathetic nervous system, which is responsible for relaxation.

When you activate this system, your body suppresses the opposite system (sympathetic nervous system) that is responsible for the stress response (e.g., the fight or flight reaction).

While you can use this technique to calm anxiety at the moment, it is best used as a daily preventative practice.

Using this breathing practice regularly helps to make the voluntary practice involuntary.

The speed with which you do the breathing practice does not matter. Instead, it is important to maintain the ratio of 4-7-8 so that the exhale is longer than the inhale.

Within just a few short minutes, this breathing technique will help activate your parasympathetic response and slow down your heart rate while lowering blood pressure.

You can use 4-7-8 breathing in many different instances, including when feeling stressed or anxious before bedtime, which is another great reason why practicing at night. Once you become comfortable with doing four cycles, you can increase to a maximum of eight cycles.

Sources - verywellmind.com