Well here's my experience of cold water therapy:
When I was 15, and in the grip of a ME relapse, I was admitted to the local mental hospital (I live in the UK, enough said).
Part of the 'treatment' protocol was exercise (naturally). As I was unable to comply with the physical demands that were initially recommended, I was prescribed weekly cold water swimming instead. Every Friday morning I was forced into the pool and, since I was too weak to actually swim, I was left to stand, up to my chest in cold water for 45 minutes each session.
Prior to my "swim" I was able to walk to the poolside. However, post-"swim", I had to be carried out of the pool and put to bed. I was virtually hypothermic, unable to move or speak, my heart beating on the go slow and blue from head to toe. I weighed less than 6st and yet it was deemed perfectly reasonable to subject a child to such torture - and torture it was. Despite seeing absolutely no improvement whatsoever in my condition, this regime was continued for 9 months.
Lucky for me, I was sprung from this hellhole by the need for urgent non-related surgery, otherwise I truly believe that cold water therapy would eventually have been the death of me.