Laughter: it's not always fun and games.

Flickr/ninasaurusrex

For many of us, laughter is a perfectly normal part of human existence: it helps us build relationships, generates good brain chemicals, and releases pent-up tension. It can even improve your cardiovascular function.

But not all laughter is healthy. For some, it's no laughing matter at all.

When Tigist Feyisa noticed her two-year-old son breaking into peals of uncontrollable giggles that left him "confused and disoriented," she grew concerned. Then she learned that Matthew's pathological laughter episodes -- gelastic seizures, in scientific parlance -- were actually the result of a tumor in his brain. "It's heartbreaking," Feyisa said. "I mean, heartbreaking to find out your child has a tumor."

Thankfully, such lesions are usually benign, and Ephrem appears to be functioning normally after being operated on earlier this month. Still, the growths are linked to all sorts of developmental and behavioral problems, even if they themselves aren't inherently life-threatening. Uncontrollable laughter is just the beginning -- patients have experienced symptoms ranging from early-onset puberty to full-blown intractable epilepsy. To date, what we know about gelastic seizures mostly revolves around how the disease progresses in patients over time. Why the tumors develop is still largely a puzzle.