I have been doing the Wim Hof method (cold showers, breathing exercise) for two weeks and it surprisingly effective in alleviating anxiety and depression. I also feel more awake.
For context, supposedly there have been done a couple of studies [1] that show benefits for strengthening the immune system.
I'd let him have his way but completely isolate him and deny him the hospital. He's over 60 and if he died, he'd be a prime candidate for the Darwin Award.