Barometric pressure directly affects your ability to breathe.
Recently several people died by asthma attack in Australia and thousands of people with no preexisting history of respiratory illness suddenly developed symptoms. The most likely explanation so far was the sudden change in barometric pressure and high pollen counts.
If atmospheric pressure decreases it shall lower your blood pressure.
http://www.mayoclinic.org/diseases-conditions/high-blood-pre...
More generally, weather has a direct effect on mood and behaviour.
http://psychcentral.com/blog/archives/2008/11/09/weather-can...