The body scan is a foundational mindfulness practice in which you systematically move your attention through different regions of your body, noticing sensations without trying to change them. Starting at the top of the head or the soles of the feet, you slowly scan downward or upward, bringing curious, non-judgmental awareness to each area. The body scan is particularly effective for reducing physical tension, improving sleep, and reconnecting the mind with the body. It is a central component of Jon Kabat-Zinn's MBSR program and is often practiced lying down for 20 to 45 minutes.

Reference:

Wikipedia: Body Scan Meditation

https://en.wikipedia.org/wiki/Mindfulness-based_stress_reduction