Well, i'm really new to all this stuff, but I've taken a crash course in it and i'm learning some interesting theories. Honestly, 6 months ago i wouldn't have known what a bija mantra or a mudra was.
Vibrations are huge part of my experience. Sometimes I feel as if there is an earthquake happening. The way i've figured it out, is that if you think about it, we're made up of atoms, right? I'm no atomic scientist but i'm assuming that because atoms themselves are a collection of swirling electrons and protons, they have a certain vibration. And if they're dense enough, they take on the form of solid matter. Which is why we appear solid, although if you think about it, we're just a mass of moving energy.
So apparently what happens when people meditate or chant certain things the sound acts as a catalyst to vibrate the atoms in your body around to alter them to some degree. Sound in and of itself can alter matter, for instance an opera singer breaking glass or loud sound breaking an eardrum. So if "energy" of some kind is intense, we can feel it's vibrations in our very being.
This is why dance is such a prominent part of ritual of ancient peoples and cultures. Because the combination of music, sound, and chanting could literally alter their physical make-up and conciousness, or so they believed.
The yogis believe chanting the mantra "OM" attunes your body and conciousness to the natural sound of the universe. Literally chanting this sound will attune your "vibration" with that of the universe. Sounds new-agy, but I swear there is something to it. the literal sounding of "OM" in theory then alters your atomic structure to make it "resonate" at another level. This in turn alters your conciousness, and the yogis believe even your physical body. They invented Hatha yoga to make the physical body more apt to this experience.
So i'm assuming the reason why i chant these sounds is that my soul speaks Sanskrit, or all our souls speak Sanskrit. If you research Sanskrit, you'll see the Indians believe it is the language of God, or at least the language of the primordial universe. So in theory, the words act as catalyst to altering not only your conciousness but perhaps even your physical reality. Because the words themselves are simply sounds that tweak atoms and in turn conciousness. Therefore these sounds are part of our being, we just don't know it, because it's a part of our being we don't ever access. I mean, we're too busy crossing the street or putting food to our mouths to be aware of it. That's why there is so much emphasis on meditation. Because then, the ego is shut down and you can focus on higher states of awareness.
I've heard of stories of people levitating and other stuff, but nothing like that has happened to me. Although to do some of the yoga poses spontaneously is quite frightening at times. I normally cannot do a headstand so It's pretty intense when it happens. A lot of it looks like Hindu temple dancing. I swore it was demons at first too!