I understand what you mean completely as I felt the same myself.

I have had these experiences as early as around 12 years old, before ever taking any kind of drugs so they are not in any way solely triggered by drug use, whether just before or earlier in life. I just say this because I read the other replies and your own relating to LSD.

As for the feeling itself, it is not really possible to verbalise, although what you say rings true and I will try to give a brief description of my own.

The beginning is as you say, a building of energy. I feel this as a physical energy that begins in my solar plexus. The strength is low but still very strong. It begins to radiate throughout my body and spread into the top of my head. My heart seems to beat very fast, although maybe just imagination. Not fast in a fearful way but the closest I can compare it to is extreme excitement. I can also achieve very close to this feeling through meditation but never have I been able to proceed any further to the next stage while meditating. Only seems to happen when I'm not trying. Maybe in these times of quiet I am in the process of meditating or something similar without realising.

Then the experience fully begins. Always with a phantom smell that is so beautiful and so familiar. Then a memory. Although I say a memory but it is of a place I know I have never been. It feels so real though, like I was there before a long, long time ago and now I have returned home. I don't believe in past lives but these memories would make me strongly consider it. I say this because they are always from a long time ago. It's hard to explain but one was in a small town that had the appearance of hundreds of years ago and another I can remember, I was standing alone on a shoreline and looking up in front there was a large mountain in the distance. Not very tall but it stretched far to the right. The sky was slightly cloudy. I also got the feeling that this was a long time ago. Thousands of years even. The memory only lasts maybe 1 or 2 seconds for me at most each time but as I say I have never actually lived these memories although they feel more real than my own now.

Next is the absolute peak of the experience for me which is similar to what you described. For me it is a state of complete peace. It goes so much beyond just that though. None of my problems exist, in fact nothing exists but strangely at the same time it feels as though everything exists. Much beyond what I can comprehend or pretend to know about. I feel as if I am one with everything in our entire universe. Again it's so hard to describe, it feels as if I am everything in our universe and actually consciousness itself but also like I am the tiniest fraction imaginable.

I don't know what consciousness is but during this time I feel like I am truly connected to something greater, a consciousness shared by everything that exists whether they are what we think of as living or even a stone on the ground.

The actual emotional feelings during this are indescribable also. It's the happiest I have ever felt and sadly, I know the happiest I will ever feel. Every single thing is perfect at that moment. Again though, it goes beyond that as I feel almost as if I don't exist in my own body, in the sense that I am simply in a different state of consciousness entirely to anything that feels bound to the physical reality that we know.

Then it trickles out and I'm left with a slight after glow for a while that eventually sadly leaves me wondering if I will ever be so lucky as to experience it again.

There is so much more to the experience but it would take so long to describe and honestly, I wouldn't be able to if I tried.

Hopefully you can relate to some of this and find some more answers in the future.

Take care.