Daylight savings time transitions and disruption of our circadian rhythm has been associated with an increased risk of stroke, heart attacks, anxiety, motor vehicle accidents. Usually the effects are more pronounced in the spring when we lose an hour of sleep in the morning but even switching back to regular time in the fall still has effects on our physiology.
Aside from changing the clocks, many body systems are impacted by circadian rhythms, including alertness and cognitive function, hormone secretion, cell function, and even gene expression. When we disrupt our circadian rhythm with artificial light at nighttime it throws off the normal cellular processes that should be happening when it is dark. Excessive night time light has been associated with higher incidence of some cancers, mood disorders, and metabolic dysfunction (that plays a role in obesity and heart disease). This can be an issue in regions where the day-night cycles vary a lot from summer to winter and plays a role in seasonal affective disorder, and can also be an issue for people that work shift work.
Luckily, changing the clocks twice per year should only impact us for about 2 days but in some people it can take up to 1 week to realign biological processes. Other times of the year, night owls may want to think about how much you are exposed to artificial light. If you are sensitive to mood issues, then try being awake with the natural light spectrum of the sun as much as possible, it has more of an affect on your brain than you may have thought.