"It was as if my body had frozen. I could hear the sounds around me, and I was conscious, but I couldn't move. Not even a finger," she recalls.

No one noticed her situation, and when they finally did, they rushed her out of the scorching hot room, called an ambulance, cooled her down with ice and fed her sugar water.

Half an hour later, she was able to get up and walk slowly, but she had struggled so hard to breathe that her chest ached the next day.

"I was scared. I felt so close to death for the first time in my life," Zhang says.

Zhang's symptoms were probably caused by dehydration and hypoxia, according to a Beijing yoga instructor Cheng Gong.

"Hot yoga is very demanding to a practitioner," Cheng explains. It is like doing strenuous activity in a hot and humid environment, and has certain health risks associated with the extreme heat, such as heat stroke, especially when the practitioner is not in a good health condition.

While Zhang's experience is extreme, it is true that yoga injuries happen more often and more easily than people think.

Cheng says students may easily strain, sprain and dislocate muscles, joints and ligaments if they don't perform exercises correctly.

Most yoga injuries are light, such as muscle strain, but there are also chronic and severe injuries accumulated over months or years because of incorrect posture. This may include injury to the cervical vertebra and spine damage, or retinal tears.

"Every asana, or yoga pose, has its mechanism and essential requirements," Cheng says.

"If students fail to get correct instruction, or if they don't follow the instructions, chances are they will end up with injuries.

"A good yoga teacher must be able to help students do the poses correctly, and not push them beyond their capabilities."

The teacher also needs to be able to detect the "danger zone" for individual learners, based on the individual's physical condition, Cheng adds.

The problem is many yoga instructors in China are not properly qualified.

Some rush into the profession only for the money, and may not have proper understanding and skills for yoga coaching, Cheng observes.

"These yoga teachers are very irresponsible," Cheng says.

Tang Xiaodi, 26, from Shanghai, has practiced yoga for nearly 10 years, and has never been injured from doing yoga.

She was surprised to hear her mother say that she hurt herself soon after taking up yoga.

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