No idea what it would do for someone with ME. However my nephew has rapid cycling Bipolar 2. He does seem to find that a swim in the sea helps. I think Bipolar 2 is basically just brain chemistry gone haywire, so maybe cold water swimming would help any neurological condition?Immersion in cold water has sometimes been mentioned as a possible treatment for many things and specifically ME/CFS in social media. There are also the traditions of Scandinavian countries and others of alternating sauna with cold water dips.
I thought it would be useful to look at the evidence and hear about any personal experiences with this.
Personally I can't actually physically get to the beach, and I can't tolerate sunlight. Might be able to do it if we could go back to the old Victorian bath huts on wheels!