Meditation - body moving himself

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Yesterday i tried meditating with hemi-sync and had very intense experience - i meditated on AUM mantra in my head, and with each breath mantra was quieter and it was going down the spine. When it reached pelvic i couldn't hear it in my head, but i feeled the vibration, and in that moment my brain felt like it was hit with lightning. I continued to meditate with similar experience, but not so intense for 20 min. On the next day when i was reading book i kinda falled into meditation, and my spine begin small movements back and forth, i didn't want to stop it. Then i've had feeling that my head was grabbed by someone and pulled up very hard, with shoulders stressed. So this was like 3 hours very hard pulling my spine, hands, legs, eyes, throat and after that i still got this, but not so intense. Question is - what is this? Is this ok?