A profound experience while meditating. What was this??

I have just had an extremely profound experience during meditation, and I would like to know what it was, and if others have had similar experiences.

So I was sitting meditating in my chair, sitting upright. Normally I sit on the ground, cross-legged, but I have issues with one of my legs getting numb when I do this, so this time I decided to sit in a chair upright. I was focusing on my breath.

About 20 minutes into the meditation, I let my awareness expand onto my feet, the sensation of my feet on the floor. And as I started to feel that, I felt this indescribable sensation. It's difficult to explain. I felt like there was this huge, huge, astronomically large presence in front of me. I think it may have been circular, like a ball. It felt loud. It felt scary. I knew I couldn't really hear it, but somehow it felt like it made a lot of noise, like it was just loud with intensity. It somehow reminded me of my childhood. I'm not sure how to explain that. It reminded me of something I used to experience often when I was a child, but since stopped experiencing. I felt like I was extremely large. It felt like my hands were enormous. It felt like I was enormous, the size of like a planet or a god or something. I felt like I was experiencing the feeling of speed, as if things were happening all at once and at a rapid pace, and yet I felt like time had stopped. The sensation of my breath felt extremely small and far away, like it was on the other side of this large presence, like I was watching the sensation of the breath from miles and miles and miles and miles away. The whole experience felt extremely, I would say, pleasurable, and I noticed a desire for it to stay with me. This lasted for about 15 or 20 minutes, and then I noticed the sensation of the size of this presence got smaller and smaller and moved away. I believe it moved a little to the left and got smaller until I found my breath coming closer to me, and then I returned to normal.

What the hell was this?! This felt like something one might experience on a heroic dose of mushrooms. I have never had anything like this happen during meditation. Something about it felt very mystical and otherworldly.