(HealthDay News) -- Periodic limb movements are repetitive movements that typically occur in the lower limbs every 20-40 seconds during sleep, the National Sleep Foundation says.

The actions may resemble muscle twitches, jerking movements or upward flexing of the feet.

Episodes of periodic limb movement syndrome (PLMS) can last from a few minutes to a few hours. While the cause is unknown, scientists think it it related to factors in the nervous system.

PLMS generally isn't serious, although it may contribute to chronic insomnia and daytime fatigue.

In rare instances, it may signal a significant medical condition, such as kidney disease, diabetes or anemia, the foundation says.