Further, there are enough examples of what might be termed ‘physiological catastrophes’ or those events where an athlete experiences a dramatic loss in body homeostasis that can potentially result into life-threatening collapses. Classic examples of such events during high level competition include Dorando Pietri's collapse at the London Olympics in 1908, the collapse of Jim Peters in the marathon of the 1954 Empire Games held in Vancouver, the collapse and death of Tom Simpson on Mont Ventoux during the 1967 Tour de France, the deaths during the cycling races during the 1960 Olympics in Rome, the dramatic staggering finish of Gabriela Anderson-Schiess in the woman's marathon at the 1984 Olympics in Los Angeles and the non-trivial number of deaths during competition (particularly from heat stroke). These examples support the idea that ‘physiological catastrophes’ can and do occur with some frequency during competition precisely because the athletes were either unwilling or unable to down-regulate effort despite dangerously high levels of strain. In the event of a pre-existing (frequently undiagnosed) cardiac disorder [41] or drug abuse, as in the case of Tom Simpson [15], the inability to regulate effort or over-ride a “central governor” can be fatal even in well accomplished athletes.
http://plosone.org/article/info:doi/10.1371/journal.pone.0002943#article1.body1.sec4.sec3.p2

The examples of athletes being able to push themselves to the point of physiological catastrophe (e.g., heat shock) is, in our opinion, testimony of their very high motivation and self-belief rather than poor regulation of effort. Indeed, these athletes seem to be able to produce efforts perceived by other athletes as impossible to sustain or not worth being produced in order to terminate the race. This interpretation is in agreement with motivational intensity theory (Marcora, 2008).
the case of Tom Simpson may be different thouigh. Indeed, amphetamines and other psychoactive drugs can reduce perception of effort so that the normal relationship between RPE and relative physiological strain is perturbed. It is therefore not surprising that such distorted information to the conscious brain could result in excessive physiological strain which, in a diseased heart, can cause sudden death.

Marcora SM. Do we really need a central governor to explain brain regulation of exercise performance? Eur J Appl Physiol. 2008 Jul 10. [Epub ahead of print]