Pain in the back from Hatha yoga?

Last night, the stars were aligned and I made it out of work before 6:00 pm, the Metro did not stall halfway home, and my wife picked me up on time. So I went to Thrive Yoga for a class of Hatha yoga — you know, my remedial class. Well, towards the end of the class, I was seat on the floor with my legs spread wide and I noticed a strange feeling in my back, deep within the muscle tissue on my left side. I noticed that I did not have my usual reach. Then, the pain became more focused, and I realized that I was having spasms, seemingly at the height of my kidneys. I waited for it the pass, and then went through the rest of the final sequences ending in savasana. No problem, except for a little discomfort in my back.

This morning, the problem was more pronounced. If I carry my shoulder bag on the right shoulder, it hurts my back; I can sling it across my chest without any pain. If I bend over, however, the pain is most noticeable.

For the life of me, I can think of any pose or movement last night that set off alarms. Marylou, the instructor, takes a lot of care to work through a progression of postures to warm us up gradually. She has her own aches and pains, and wants us to avoid them if at all possible. The one thing is that we were working to loosen up the thoracic spin and rib cage, which I know is pretty tight in my case.

Add to all that a bruised left heel, stiff thigh muscles and soar sit bones, and I am feeling my age.