Both of these techniques use breathing and your brain to calm you down. Meditation is more about centering yourself, as well as being mindful and aware. Visualization is all about the fact that your brain doesn't know the difference between visualizing things and actually living through stuff. These strategies can help with stress. Since I am not an expert, I would like to encourage you to check out online videos that guide you through these strategies. Check out YouTube or my Facebook page to find some videos.
