It's common for people with Parkinson's disease to complain of excessive drowsiness during the day. Several factors are to blame. One is that, for various reasons, most Parkinson's patients don't get enough sleep at night. When levodopa or dopamine agonists wear off in the nighttime, symptoms of stiffness, tremor, and slowness of movement resurface, says Kelly Lyons, a research associate professor of neurology at the University of Kansas Medical Center in Kansas City. A severe tremor might wake the person, as might stiffness as he tries turning over in bed. Or discomfort may keep him from falling asleep to begin with.

Another complication is that Parkinson's patients tend to suffer from sleep disorders:

• Sleep apnea -- interrupted breathing episodes during slumber
• Periodic limb movements -- repeated jerking motions of the legs while asleep
• Restless leg syndrome -- uncomfortable tingling or crawling sensations in the legs, causing an irresistible urge to move them during sleep
• REM sleep behavior disorder -- "acting out" of vivid dreams, sometimes leading to punching or kicking of bed partners

What's more, studies show that Parkinson's drugs have sedative effects, says Lyons. The challenge is to try adjusting the medication dose or scheduling, or switching to another drug, while still keeping motor symptoms well controlled. Other medicines prescribed for anxiety, depression, and psychosis can also cause daytime sleepiness. Altogether, Lyons says, "the whole sleep cycle is just really messed up" for the Parkinson's patient.