Asking that question is the simple part. I am more curious what he actually does afterwards to reduce the stress..
It never feels like i have to plan my vacations around work, and my previous manager was very strictly insisting on no emails or comms while you were on vacation, and i loved how it actually worked out.
Relatedly, I've heard that in Helsinki they have some mobile saunas which are parked in front of businesses which are available for stressed out employees... not sure how true it is.