Yoga done wrong can be dangerous and can cause adverse effects on your overall health. Some of these side effects as are follows: Adversely effecting your muscles and cause heavy pain and internal bleeding. Some yoga poses can even lead to fracture or ruptures of delicate bones. This case is especially true if you have delicate or brittle bones. Ruptures like these can take months to heal and might sometimes even need surgical intervention. Some yoga poses can even lead to adverse gastric problems in some individuals. Most people complain gastric symptoms to be associated with hatha yoga postures. This is especially true if you do not perform all yoga asanas in a particular sequence. Some of the yoga poses are so complex that even experts don't understand them properly. For instance the kundalini yoga. Yoga poses like these done wrong can have adverse effect on you mentally. This is known as the kundalini syndrome. The possible side effects on kundalini syndrome are pseudo death, psychosis, pseudo psychosis, confusion, anxiety, panic attacks, depression, sadness, suicidal thoughts, urges to self-mutilate, homicidal urges, arrhythmia (irregular heart beat), exacerbation of prior or current mental illness, insomnia, inability to hold a job, inability to talk, inability to drive, sexual pains, temporary blindness, and headaches. Even if you practice yoga under a well certified instructor, chances are that he or she is not fully aware of the techniques and might give you wrong instructions. So you need to be super careful if you even consider attempting these advanced yoga forms and practices, listen to your body, share your experience with your teacher so that they can help you guide you, inspire you and understand you better.
There are no shortcuts in Yoga so be careful, do not modify it.
Follow the system, if you keep using your mind in yoga is not for you.
Please respect the tradition and true wisdom of Yoga.
Be safe be healthy..