Some sleep disorders may be related to other conditions. For instance, REM sleep behavior disorder, or RBD, is often associated with neurological conditions such as Lewy body dementia, Parkinson’s disease and multiple system atrophy. Related conditions to insomnia, meanwhile, include psychological disorders such as stress, anxiety and bipolar disorder, as well as health conditions such as arthritis, overactive thyroid glands, gastrointestinal disorders, Alzheimer’s disease, Parkinson’s disease, sleep apnea and restless legs syndrome. Also, a form of sleep apnea called central sleep apnea, which occurs when the brain does not send the proper signals to the muscles that control breathing during sleep, is usually caused by heart disease. This type of sleep apnea patient is likely to remember waking up.