Actually it feels more like a sudden involuntary loss of sense more than anything. If it's a really bad one, I lose touch with my self completely and collapse physically and mentally (the correct term would be fainting). I'm orthostatic intolerant so I get them very frequently and have been for most of my life.
The rainbow in itself is just light refraction; nothing too spectacular after you see quite a few. If you want to get into religion, they have the rainbow as symbolism among the different branches of religion.