Daytime napping may not be a good idea for people with fibromyalgia, a chronic condition that causes unexplained pain.

A survey of more than 1,000 patients found that those who took more frequent and longer naps had the worst symptoms, according to the journal BMC Musculoskeletal Disorders. Taking naps was also associated with higher levels of depression, anxiety, fatigue, memory and sleep problems, and these worsened with naps longer than 30 minutes.

People with fibromyalgia may use daytime napping as a coping strategy to manage symptoms, but the researchers from the University of Groningen in the Netherlands say there should be more guidance about this, as it appears to make the condition worse. Napping disrupts nocturnal sleep patterns, which may make symptoms worse.