This is one of my symptoms.
The "bloating" as my physio explains it, is simply gravity, so don't worry much about it. My own stomach is relatively flat when I wake up, and by the end of the evening I look fat.
Claire Weekes is absolutely right: and
@Diana-M is correct to point this out - this is anxiety breathing and part of the fight/flight mechanism. You are stuck in fight/flight which is absolutely part of TMS. This is way your own nervous system is trying to keep you safe. It's very similar to the startle reflex in infants.
I know you don't feel anxious, but I guarantee, you are anxious and stressed. That's what TMS is all about. You are simply not aware of this state because it has become the normal default for you and you've probably been here for a very long time.
As part of my own healing, I utilize a specific form of physio therapy that recognizes this type of breathing. I'll offer you their very first technique to begin to be aware and be able to drop into your body and simply breathe.
Sit in a chair, with upright posture. Not stiff, but similar to the posture prompted in meditation. Relaxed but upright.
Close your eyes and simply breathe. Notice the cool air going in, warm air going out. Notice if you breathe through your noise or mouth. Slowly focus on nasal breathing if you use your mouth.
No forcing, no worrying if it's right or wrong. You are noticing which is a passive state.
Keep this breathing up for 10 or more breaths, and see if your exhale naturally slows down. Don't change or force it purposefully. Keep breathing.
Now put your attention on the top of your head, and simply notice the skin of your scalp. Can you sense that it is alive? Maybe you sense a tingle, or the air around you, or the temperature. Breathe 3-4 more breaths without counting. The number of breaths doesn't matter. Slowly.
Now notice your eyes. Can you make slow and gentle mental circles around your eyes - almost like a mental massage. Breathe 3-4 more times, slowly. Don't try to relax, don't try anything except to gently follow instructions. Now move this method to your mouth and then jaw.
After this, move your attention to your chest.
Can you notice without changing anything at all, that the muscles of your chest almost imperceptibly move when you breathe. Keep breathing, keep noticing. Notice now the sides of your chest. Then notice your upper back and see if you feel anything at all move or have any sensation at all. Just breathe slowly in and out. Change nothing, no forcing. Notice gently.
Now drop your attention to the bottom of the rib cage and do the same exercise, now drop it to your belly. When focusing in the belly do not force any air into the belly. Just notice. Nothing more.
This takes 10-20 minutes to complete. Do it sitting for a week or two then try different positions like laying with knees up and small pillow under head, or knees over the side of bed or sofa...
If you desire to change anything, force anything etc. that is anxiety. Notice if your mind worries if you are doing this "right", or wants wander or anything else. All of this is OK, but signs of anxiety and that is perfectly fine. You can be anxious, it's no big deal.
This exercise is nothing but a form of gentle brain retraining through noticing.