Hi. It can still be the sedative that was used. The medicines we take are processed through enzymes found primarily in our liver called cytochrome p450. We are not all created equal in how these enzymes function. If medications are combined on possibly an already strained enzyme there could be a fall out.

This article explains about headaches

http://www.achenet.org/resources/dru...h_for_and_why/

This article explains the p450 and lists drugs you may have taken and which enzyme would be used to metabolize

http://www.drugguide.com/ddo/view/Da..._Should_I_Care