Hot Cold Water in Shower/Head Massaging

I remember hearing people telling me stories of people in the "old country" jumping in lakes or rivers or whatever to cool off after a hot summer day and die? Is this true? Or only for people who maybe had an unknown heart condition? Is it safe to do this in the shower?

And head massaging is not going to cause blood clots right?
Thanks

well if you had a heart condition or real high blood pressure maybe be careful, or start slow otherwise perfectly safe. I Like taking scottish showers myself and it has health benefits
http://en.wikipedia.org/wiki/Sauna#With_cold_exposure

immersion (or showers) has the added benefit of improving the body's anti oxidant capabilities, with increases in glutathione and reduction of uric acid.

A reported study from the Thrombosis Institute in London into the effects of the cold bathing found that volunteers that followed a disciplined daily regime had increased immune white blood cells and the level of the body's natural blood thinning enzymes substantially increased, improving micro circulation. It also stimulated the production of hormones such as testosterone in men, and boosted women's production of estrogen