Probability

I'm having trouble with probability. It seems simple enough: you have a fifty percent chance of getting heads with the flip of a coin. There is a 25% chance of flipping heads twice and so forth. Where I get stuck is that although there is a 25% chance of flipping heads twice, if I flip heads once, on the next flip there's 50% chance of flipping heads on this go around. Mathematically it makes sense and is almost childish in it's simplicity. But the point of probability is not only mathematical prediction, but a way to describe and understand our environment. Unfortunately it goes against the value I place on it. Past probability has no impact in present probability. Although I can predict a 25% chance of heads twice, it has no bearing on the moment of action.

How does this affect me? Let's say that there is a 25% chance of your head exploding if you drink a pint of Jaeger mixed with espresso and hot sauce. This is based on observations of things that occur in the past. Based on this percentage I think, well shit, there's 3/4 of a chance my head won't explode so pour me a drink! Although rationally I know that this bit of "science" carries no protection, irrationally I don't act this way. I use percentages as a protective guide as if these past events shape the present.

The thing that really gets me is what are my chances? My father had a heart attack at 38 and died of heart disease at 57. I eat differently, don't smoke, minimize time on my ass but I have a high stress job. If 5% of people in my situation have an MI, does that mean I have a 5% chance? Or do I have an X% chance that in the grand scheme of things only carries meaning as a single mathematical point in thousands observed from afar?