"I suddenly become conscious and that I am still chanting the mantra. I wonder whether I was asleep or got hypnotised or something else."

This is a very highly studied form of an Alpha state; experienced meditation practitioners can easily and quickly slip in and out of this state. While hypnotism has been broadly debunked, alpha states are created to put the mind in a highly suggestive state which can be conducive to taking in learning or other suggestion. There are other ways to induce this state of alpha waves thru repetition of sound, light, images, etc. Chanting is a great way to enter this, in fact, tent revivalist ministers, whether they understand it or not, speak in a cadence that can lull their audience members into an alphastate. I believe there is also a state where the brain is predominantly theta waves, which would be even deeper and more relaxed, perhaps you got that far. For the record, most daily waking activity is done in a beta state, predominantly beta waves. Not much supernatural to this I'm afraid, it can be reproduced in other fashions. There is a pretty large focus though on learning among people trying to sell you alpha inducing products or techniques, so there may be something to that.

Doing Sadhana without a Guru might I add. Kundalini arousal without the appropriate preparations is very dangerous to the body and mind. It's f*cking with your life force, for a lack of better words. Gopi Krishna is one person who lived and had a very intense and painful experience trying to improperly awaken Kundalini. There are many people who have testified with the same symptoms of improper sadhana and Kundalini arousal... And some of them don't even know about these symptoms to just imagine them. Why would so many people experience the same thing if it was just a wives tale? There are mental and physical imbalance and dis-ease, there can also be disease and imbalance spiritually and with other systems of the embodied person.

Almost everything is a wive's tale to you anyway...