i can report from a personal experience of hypothermia for a few hours, in water. it's uncomfortable, mostly until you get all you limbs in/they completely get cold. at a certain point, you don't really feel it anymore, or anything. i got completely scratched by rocks and all i felt was a little pressure on my knees, soon to find them completely scraped and bleeding (after i got out). It definintely isn't for the faint of heart, and if it takes too long SI can kick in, and your survival mind will start to go in place. no matter how strong you think your will to die is, it is never above your SI. When it truly comes down to it in the end, your body will do anything to survive.
i hope you find some peace and feel free to ask any questions :)