I didn't know where to ask this but i've heard that sometimes Navy Seals die during traing? Is this true? The same goes fro Green Berets.
Your question was prophetic, coming as it did on May 16th. Here is a link to an article in the New York Post about an occurrence of this sort on May 17th.
It seems to happen "accidentally," as opposed to "overtraining," but yes, it does happen.