The mistake: For some people, intense sexual pleasure (solo or partnered) leads to an emotional letdown that can last for up to six hours. These "post-coital blues" aren't totally understood, but psychiatrist Richard Friedman at Weill Cornell Medical College in New York speculates that the amygdala, the "emotional" brain region that's inactive during orgasm, strongly rebounds afterward—triggering sadness or crankiness.
What to try: While Friedman has treated this condition with antidepressants (known to curb the orgasmic high—which in this case isn't such a bad thing), you might just stick to hugging and kissing. This type of physical contact prompts the release of oxytocin, which can increase positive feelings like trust, generosity and closeness...otherwise known as "love." (Clinical trials are exploring the role of oxytocin in treating clinical depression.)