In a Yin Yang yoga class we work with both qualities because active, dynamic movements (Yang) are alternated with stilling postures (Yin) that are held longer just like in the Yin classes. The Yang in the movements is focused on the muscles and provides a powerful vital body. The Yin postures focus more on the deeper connective tissue around joints and organs and brings you into contact with the silence within yourself. This creates a healthy balance between body and mind.
Pay attention if you are pregnant or have just given birth, always let the teacher know. Since your body is soft it can be harmful to go deep in the postures.
Yoga nidra, meaning "Yoga sleep", is a form of yoga where you relax in savasana and the teacher guides you through a meditation into a deep state of relaxation. In this state, between sleep and alertness, deep healing takes place. During Yoga Nidra your brain goes from beta brain waves (an awake state with a lot of brain activity) to alpha brain waves, a more relaxed state. With the alpha state, the mood-regulating hormone serotonin is released, and that calms you down.
From alpha, you go through a theta brain wave state, (the dream state, with 4 to 8 thoughts per second) to a delta brain wave state, where your thoughts are only 1 to 4 thoughts per second. In this state the stress hormone cortisol is removed from your system. Finally, you can drop to a deep delta state, where your brain is thoughtless. During Yoga Nidra you learn to stay alert, even when your body is asleep.
You can sometimes fall asleep during Yoga Nidra, but gradually you will notice that you will remain alert through practice.