Stillness
Excessive thinking is the cause of most, if not all of your disease. Breathing and thinking are connected.
Your stressing mechanisms, the adrenals, the vagus nerve, your autonomic system that hypes you up or calms you down are connected to your thoughts. Pay attention to your breath and rest in the spaces between breaths and your thoughts still. In fact it is difficult to think in the space between thoughts, all you can do is relax.
Try this:
breathe in stop, wait and drop into a relaxed moment notice that when you relax the thought or thoughts you were experiencing have momentarily stopped
then exhale and repeat a few times
when you are comfortable with that, and that might take a few breaths or a few sessions over a few days, then exhale and hold your breath out and drop into a relaxed moment. I find that the most profound mental and physical changes take place.

To over come your resistance to stopping may seem hard and you may feel hard pressed to put the time aside to relax or meditate, but all you need is the space between breaths occasionally to connect with stillness and healing.
The only thing your body is attempting to do is regenerate and heal but you get in the way and resist the stillness that is half a breath away.

The Vijnana Bhairava Tantra, (a yoga text) is a love song between Devi and Bhairava, suggests about 112 ways to achieve stillness,

“When the ingoing pranic air and outgoing pranic air are both restrained in their space from their (respective points of) return, the essence of bhairava, which is not different from bhairavi, manifests. (the negative and positive pressures of your body become neutral)

When Shakti in the form of vayu or pranic air is still and does not move swiftly in a specific direction, there develops in the middle, through the state of Nirvikalpa, the form of Bhairava.” (the pressure or stressful forces in your body quieten into enlightened stillness because they can only go in that direction)