In the US we get an extra hour this Weekend
More on the dates for both US and EU here:
and an interesting look at circadian rythms here at Scientific American:
The problem is, many of us do not set the alarm clocks during the weekend. We let ourselves awake spontaneously on Saturday and Sunday, which allows our circadian clock to start drifting – slowly phase-delaying (because for most of us the freerunning period is somewhat longer than 24 hours). Thus, on Monday, when the alarm clock rings, the gradual rise of cortisol, heart rate and blood pressure will not yet be as far along as the previous week. The ring of the alarm clock will start the process of resetting of the circadian clock – but that is the long-term effect (may take a couple of days to complete, or longer.).
The short term effect is more dramatic – the ring of the alarm clock is an environmental stressor. As a result, epinephrine and cortisol (the two stress hormones) will immediately and dramatically shoot up, resulting in an instantaneous sharp rise in blood pressure and heart rate. And this sharp rise in cardiovascular parameters, if the heart is already damaged, can lead to a heart attack. This explains two facts: 1) that heart attacks happen more often on Mondays than other days of the week, and 2) that heart attacks happen more often in the morning, at the time of waking up, than at other times of day:
Please click out, several good charts at the link.