Laughter may be the best medicine, and science suggests it may be a pretty solid sleep aide, too. But sometimes nighttime mirth isn't always a laughing matter. Here's our take on the pluses, and a couple minuses, of laughter and sleep.

Laughter Busts Stress

There's not a lot of direct research on the topic of laughter and sleep, but recent research shows laughter has numerous health benefits, particularly as we age.

According to an overview published in Canadian Family Physician, several studies show laughter (and its instigator, humor) to be effective stress relievers. The less stress we feel, the better we can fall and stay asleep. Feels like a good excuse to keep a joke book on your nightstand as part of your bedtime routine.

Researchers from Georgia State University found that adding simulated laughter to a senior exercise program could improve older adults' mental health, aerobic endurance and their confidence to finish the workout, according to a recent study published in The Gerontologist journal.

Another study of seniors, by Loma Linda University presented at a meeting of the Federation of American Societies for Experimental Biology (FASEB), found laughter may lower cortisol levels and enhance memory. Healthy seniors and those with diabetes were shown a 20-minute funny video to determine if humor would affect their memory. Compared with a control group not shown the video, those who watched the funny video scored better on memory tests and also reduced their cortisol levels significantly.

"It's simple; the less stress you have the better your memory. Humor reduces detrimental stress hormones like cortisol that decrease memory hippocampal neurons, lowers your blood pressure, and increases blood flow and your mood state," explained study co-author and long-time psychoneuroimmunology humor researcher, Dr. Lee Berk, at the FASEB meeting.

It's worth noting that in a 2007 study published in The Journal of Psychosomatic Research, Japanese researchers found that watching a humorous video before bedtime could increase melatonin levels of nursing mothers. Melatonin is a hormone that helps regulate the body's sleep and wake cycles. In healthy individuals, melatonin levels start to rise in the evening, getting the body ready for sleep.

Half of the participants in the Japanese study had atopic eczema. Patients with atopic eczema often have decreased blood melatonin levels, and report sleep disturbances.

Sleep-laughing Response to Dreams

Sleep-laughing is known as hypnogely, according to a small study referenced by the National Institutes of Health. A total of 10 patients observed while sleeping experienced hypnogely, with nine laughing during rapid eye movement (REM), the early sleep stage when dreams occur. In most cases, sleep-laughing is a harmless physiological phenomenon, a behavioral response to dreams that are “odd, bizarre or even unfunny for a person when awake."

The study authors noted that in a minority of cases, sleep-laughing may point to neurological disorders affecting the central nervous system. In these patients, the sense of mirth is absent while sleep-laughing.

Laughing Outbursts Linked to Serious Issues

There's a serious side to laughter and sleep. Laughing (or crying) outbursts out of proportion to the triggering event could be the result of a brain injury or serious underlying condition. Known as the pseudobulbar affect, or PBA, several neurological conditions may be to blame, including stroke, Parkinson's disease, dementia, brain tumors and multiple sclerosis, according to the American Stroke Association.

Episodes of uncontrollable laughing or giggling – known as gelastic seizures, according to the Epilepsy Foundation – may also be a symptom of another serious but rare tumor known as the hyphothalamic hamartomas, or HH. The condition affects 1 out of 200,000 children and teenagers worldwide.

But, for most of us, laughter is indeed good medicine.

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