Dear MrSteroids1,
I can relate! I've mixed quite a few strong psychedelics in my wild youth and had my share of consciousness-sucking black holes in the bathroom, etc., although my experiences were overwhelmingly positive and encouraged me to seriously pursue my yogic path. Yoga eventually gave me what I had been seeking through psychedelics, and more.
The narrative you expressed about God and the Self and the little self is, as far as I know, technically true. But the part you left out is that the One became many for the sake of reunion - for Love! For enjoyment of God, life, ourself and other persons. "Illusion" is just terminology; no need for despair. It simply is what it is.
FWIW, there are different approaches to so-called "enlightenment." There is monism, where the self is utterly gone, in stillness, silence and peace - Brahman. And there is dualism, where the self remains just enough to enjoy the ecstatic process of losing oneself in God, all the while still knowing that God is the only Reality - Shiva and Shakti, Krishna and Radha. You can find variations on these themes in the various religious mythologies and traditions. People will argue tenaciously about which approach is "better" but IMO it's a matter of personality, mood and temperament. We can enjoy hanging out in one state or the other as we wish.
As far as "going forward with your spiritual journey," it's kind of an organic process which will unfold as it should. A plant doesn't stop growing because it is worried that it might not like blooming. As far as whether or not "oneness with the whole is a good thing" - too late! You're already one with the whole. There is nowhere else to go. So-called "enlightenment" is just the process of realizing what is already the case.
So, I would recommend:
1. Lay off the psychedelics (which it sounds like you already decided to do so).
2. What Bodhi said, above re: grounding activities, enjoying the simple things in life, etc. (well said, Bodhi!).
3. Explore your relationship with God in whatever tradition/manner works for you - father/mother, friend, Lord, lover - whatever. You can always dissolve back into utter oneness if you want, but meanwhile, "Love casts out fear." Remember why we became many.
4. When you are ready, simple yoga practices like deep meditation. But, not yet. Especially if you are still having hallucinations or similar phenomenon, concentrate on grounding activities for now.
I promise there is really nothing to be afraid of. We can trust the process as it unfolds. You just had a really intense jolt from having that experience without the tools/context to properly integrate it. Others have been there and we survived and grew from it. You're not alone.
Thanks for your contribution to the AYP forum! Please stay in touch and let us know how you're doing and don't hesitate to ask questions. Much LOVE to you!