Getting enough sleep is always essential for optimal performance and functioning.

But service members know that a full night's sleep is not always an option. On deployment, many things make sleep a challenge, including combat operations, long work days or 24-hour watch duty.

Service members on deployment may be anxious, concerned about their own safety or missing home. And they may face uncomfortable sleeping surfaces and unusual sleep-wake cycles.

"Sleep is an inherently vulnerable state, and in operational environments there are many factors that can make it difficult to initiate or maintain sleep," said Army Lt. Col. (Dr.) Scott Williams, director of the Center for Military Psychiatry and Neuroscience (CMPN) at the Walter Reed Army Institute of Research in Silver Spring, Maryland.

Prior traumatic events or mild traumatic brain injury can also lead to additional sleeping problems.

As a result, getting proper sleep is a luxury that many service members may not always have.

"On average, military personnel sleep approximately six hours" a day, said Dr. Tom Balkin, a senior scientist at the CMPN's Behavioral Biology Branch.

An average of six hours of sleep isn't enough – at least seven hours is recommended, Williams said.

Running short on sleep could lead to poor health or poor performance. Sleep disorders can be "significant threats to readiness and lethality," according to the Walter Reed Army Institute of Research's Behavioral Biology site.

Prioritizing sleep during deployments is key to better performance, and, in the long run, a healthier military experience.