[maj0rhn]

Please. "Plain old heatstroke" -- in northern California in springtime? The high temperature for that day was 63 degrees, according to: http://www.timeanddate.com/weather/usa/berkeley/historic

It was not heatstroke.

"Going beyond your physical limit" -- what, exactly, does that mean? Thousands of times a day, people get on treadmills in cardiologists' offices, and are taken to their physical limit with a "maximal effort stress test." Even this doesn't precipitate life-threatening complications unless cardiovascular disease is present.

There are some genetic blood disorders that can cause sudden death during extremely heavy exertion (e.g. professional football drills) at altitude, but they are very rare in caucasians, and Berkeley's hills don't qualify as "altitude."