Oh, those summery days of spring! The sun is warming up for its main gig in a month or two, beads of sweat are forming on your forehead, and you’d like nothing better than to cool off somehow. How about taking a dip? Be very careful if you do, warns Dr Stefan Linsler, the German Lifesaving Society’s (DLRG) federal commissioner for diving medicine and a neurosurgeon at Bayreuth Hospital. Why? Because a heated-up body and cold water – large bodies of water in particular can still be quite cold in spring and early summer – is a dangerous combination. It puts a strain on the cardiovascular system,…