I'm writing a recent shipwreck location.  In this location, there will be slightly disfigured bodies floating around in the water.  I want to make the party members that see these bodies have to make mental composure check to not freak out while underwater, causing an immediate need to resurface for the day.  However, I don't know if there is a saving throw for this kind of instance.  Is there?  If not, what do you commonly use?  I figure it's probably constitution, but I'm not totally sure.