Yin yoga has also been my primary practice for the past month. In yin yoga, you hold gentle floor poses (seated, prone, or supine) poses for several (2-5) minutes. Holding the stretches for so long encourages my muscles to really just kind of melt into the pose. It seems to be a magic bullet for my back pain. The long-held stretches are doing wonders for keeping my back muscles relaxed and the spine healthy. I am almost completely pain-free most days.
Recently I have added ujjayi breathing with breath retention to the yin yoga practice: breathing in for 8 counts, holding the breath in for 4 counts, breathing out for 4 counts, holding the breath out for 4 counts. In this way 2'45" (the current length I am holding each pose) takes about 10 breaths.
It is said that the real purpose of the asanas is to prepare the student for meditation. That certainly seems to be true of yin yoga. Sometimes in this practice, I find my mind disturbed with unrest. Not full-formed thoughts exactly, but a jitteriness or prickliness that is hard to describe. Maybe "mental white noise" comes closest as a description. I find myself irritated at the music I'm listening to (I often play Pandora's Spa Radio station), wishing I could get up and skip forward to the next song. Unrest.
I have experienced similar sensations at times when I meditate.
Then sometimes when I'm doing yin yoga my mind is calm and untroubled, peaceful and relaxed. This I have experienced many times during meditation.
One thing I would like to do, but haven't found time for, is meditate for at least 40 minutes after my hour-long yin yoga session. I bet that would make for a nice, deep meditation. I had hoped to do that last night, but traffic was slow and I got home later than I expected. I'm not sure I'll have time tonight, either. Soon, I hope.