I've been practicing mindfulness of the breath in my abdomen for roughly 8 months, and recently realized that, while almost all instruction I have been given has said not to control the breathing in any way, I was still, in a subtle way, making my breath deeper.
After making attempts to just let my breath proceed completely naturally, I have noticed that my breath becomes very light, and I hardly feel any overt sensations in my abdomen at all. There is some element of sensation but it is not nearly as strong as typical sensations of touch. This makes it a lot more difficult to place my attention directly on the breath (but nevertheless I feel my meditation is better now that I am not controlling the breath than it was previously).
If I am wearing a shirt that is right against my abdomen, I can focus on the sensation of my abdomen hitting my shirt as I breathe, which helps. The sensations in my nostrils are also rather weak unless I am breathing with some vigor.
Is this common? I don't know what to do when this happens.
A lot of time people breathe so calmly during meditation that at first it can be a little startling. One might suppose that one could easily stop breathing altogether. But this doesn't happen. Actually, (unless you have sleep apnea) people tend to breathe very lightly like this during a lot of the time they sleep.
The purpose in meditation on watching the breath is to calm the mind.
If your mind is calm, you can begin to just let it rest in its natural state.
Does that make sense?