I would get something very similar when I was a child. I've mentioned this on the forum before. Ann Shulgin described something similar in ione of the chapters in the first half of PIHKaL. Sometimes I would wake up in the night and feel simultaneously tiny, as you describe, and also huge - and also polar contrasts like completely inky black and clearest white, completely smooth and thoroughly crumpled, all simultaneously and paradoxically seemingly rapidly alternating as well. There was always this impossible to describe visceral sensation, like "being inside my own teeth and bones. All-in-all I found it enjoyable for all its bizarreness.
While it faded away as I entered adulthood, I have had it recur spontaneously, although less intensely, a few welcome times in recent years. It always seems highly 'existential' to me, if that makes any sense.