Anxiety, asthma, depression, and many other disorders have a large unconscious component to them. Heart-rate, muscle tension and many painful or lethal factors play into them and cause numerous complications. Thankfully, the technology of biofeedback has began to unravel ways to consciously guard against these things.
What is Biofeedback?
MayoClinic.com describes biofeedback as
[…]a technique you can use to learn to control your body’s functions, such as your heart rate. With biofeedback, you’re connected to electrical sensors that help you receive information (feedback) about your body (bio).
This feedback helps you focus on making subtle changes in your body, such as relaxing certain muscles, to achieve the results you want, such as reducing pain. In essence, biofeedback gives you the power to use your thoughts to control your body, often to improve a health condition or physical performance 
More generally explained, Biofeedback is where someone works with a patient to develop coping strategies to manage a normally-uncontrollable bodily function. A great example is this paper  which details a method for managing heart rate within five treatments.