No adverse effects. Inhale through your nose, hold for a few seconds and exhale through your mouth is very good for relaxation.
Deep breathing is one of the best ways to lower stress in the body. This is because when you breathe deeply, it sends a message to your brain to calm down and relax. The brain then sends this message to your body. Those things that happen when you are stressed, such as increased heart rate, fast breathing, and high blood pressure, all decrease as you breathe deeply to relax.
The 4-7-8 (or Relaxing Breath) Exercise:
This breathing exercise is utterly simple, takes almost no time, requires no equipment and can be done anywhere. Although you can do the exercise in any position, sit with your back straight while learning the exercise. Place the tip of your tongue against the ridge of tissue just behind your upper front teeth, and keep it there through the entire exercise. You will be exhaling through your mouth around your tongue; try pursing your lips slightly if this seems awkward.
Exhale completely through your mouth, making a whoosh sound.
Close your mouth and inhale quietly through your nose to a mental count of four.
Hold your breath for a count of seven.
Exhale completely through your mouth, making a whoosh sound to a count of eight.
This is one breath. Now inhale again and repeat the cycle three more times for a total of four breaths.
If breath holding works for you then that is great. I,m glad you found, at least in part, a solution.