what is sleep regression

Sleep regression is a period of time, usually about two to four weeks, when a baby who's sleeping well suddenly has trouble settling down for sleep. It is a sign of developmental progression and often happens when a baby's brain and body are busy learning new skills. Common ages for sleep regressions in babies are around 4 months, 8-10 months, 12 months, and 18 months, with some common regressions during the toddler years around 2 years and 3 years. Signs of sleep regression include more frequent night waking, trouble falling asleep at bedtime, increased fussiness, and suddenly resisting naps. Sleep regressions can be caused by various factors such as neurodevelopmental maturation, sleep- onset associations, the need for a schedule adjustment, illness, teething, and travel or other changes in routine