So, assuming you have had a physical and gotten checked out, you are writing to the anxiety forum. That's a little telling. I've had that chest tightness, shortness of breath feeling when very anxious. Could this be you? Have you been told to look into anxiety? It really CAN cause physical sensations. And I get anxiety at night. My hormones actually depending on the day can make it much worse at night. My doctor says this is normal. I'm a woman and don't know if you are male or female. When you say you are completely not breathing during your sleep, how do you know that? Most with sleep apnea aren't fully aware. If they are labeling it anxiety, what about going ahead and seeking an assessment for that from a psychiatrist/psychologist? Then if it IS related, you could be taking care of the chest/breathing/sleep issue? That would be what I did.
Have you discussed the possibility of sleep apnea with your healthcare provider. I am not sure what country you are writing from, but a sleep study would be extremely helpful in ruling out many things.