Sometimes an overwhelming urge will start one for me, like when I feel tiny and and sort of non existant..In the grand scheme of things.
Sometimes feeling small and frail in comparrason to the rest of the population of the world, starts me on a feeling of dissociaion...
I find this all so hard to put into words.
I know this isn't a religious website, but in my case, if I didn't have my faith, life would have no meaning. Whenever I feel as you described above, I reflect on my conviction that my life followed God's plan. The peaks and valleys were necessary checkpoints, along the journey. Some of the valleys were exceptionally deep, but still had to be crossed. I'm grateful for them all. Hang in there.