Mindfulness meditation has been a positive and calming experience for me. Sometimes with a discernible difference in thinking, after finishing.
I prefer using headphones.
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I use these freely shareable mindfulness resources, that are under a Creative Commons licence.
Generally coming back to two meditations from the list:
If needing some grounding, a body scan can help.
Fifteen minute body scan - Vidyamala Burch, Breathworks
If stable and grounded, the Mountain meditation is a nice exploration of impermanence.
Mountain meditation - Padraig O'Morain