In my last post, I gave hint about how different siddhis possible with Yogic practices. Kumbhak was given as an example. It was also suggested that, you do it under the personal supervision of experienced Yogacharya. Mass Yoga congregations,shibirs are not supervision and guidance.
Sharing old post on it:
I want to do Pranayama. Can I start now?
No. You must follow pre-conditions. Or else, you will face the random unforeseen consequences due to imbalance of mind, body and prana.
अथासने दृढे योगी वंशी हितमिताशन ।
गुरूपदिष्ट मागेण प्राणायामान्समभ्यसेत् ||
Once by body postures, you achieve control over bodily movements and your food habits are balanced (right food and right time), then only one should learn Pranayam from experienced Guru.
Even if we can achieve pre-conditions in this life, worth 
🙂.
Mind you: Pranayama is not breathing exercise! It is much more than it! 🙂You can learn breathing. That is also we do very inefficiently. But do not call it ‘Pranayam’ 🙂
