Why is my body not doing what I want? Why can’t I sleep, why can’t I shake inner fears? Why – because it never does, or did, what you want. You are not your body, you are the conscious-aware-miracle experiencing the world through it. Your body is beyond your total control.
For instance – how does your heart beat? Do you regulate every pump? How does your brain choose which memories to surface? Do you dictate every thought in your mind?
Understanding the subconscious, and the deeper nature of your body, you can perform actions which lead (through trickery or chemical reaction) your body to respond in a certain way. But this must be regular, for chaotic as it sometimes is, the body is also prone to systems.
Why? Because you have not adequately trained yourself yet. Break those bad habits.