There are multiple layers of complexity within yoga. On the one hand, there are poses that are physically challenging to any yogi. On the other hand, the holding of poses for longer periods of time can be mentally and emotionally challenging. Poses may be physically difficult because they require a great deal of strength, balance, flexibility, or quick movements from pose to pose. The faster a participant moves through a sequence, the more demanding it is.
Not to downplay pampering, but self-care is more than taking bubble baths and drinking hot tea. We often take a narrow view of self-care, seeing it as spoiling oneself or indulgence, perhaps even in ways that are counter to long term health.