Re: shortness of breath feeling
It's probably because you're focused on it that it's happening. After you fell asleep your breathing continued without your help as it always will. When you're awake the tension returns and with it all your tense muscles including chest wall muscles. Anxious and fearful people tend to shallow breathe and only use the top part of their lungs. This alters the balance of carbon dioxide and oxygen levels in the blood stream and can make some people feel lightheaded and feelings of suffocation.
Breathing exercises do help but only if you do them correctly, otherwise they can make you feel worse or have no effect at all. Yoga is pretty good for teaching good breathing. Singing can also do this.
Check that it isn't a side effect of your meds too, some doctors refuse to acknowledge drug side effects and dosage.
ISB ☺
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Without fear there cannot be courage - Christopher Paolini