When your baby suddenly starts waking more at night, it can feel confusing and demoralising — especially if sleep had been improving. The good news is that sudden changes almost always have a reason.
Quick Answer
Sudden night wakings are often linked to a sleep regression, developmental leap, teething, separation anxiety, illness, or a schedule that needs adjusting.
Common Causes of Sudden Night Waking
Developmental leaps and regressions are the most talked-about cause. Around certain ages — particularly 4 months, 8 months, 12 months, and 18 months — sleep can become lighter or more disrupted as your baby's brain develops rapidly. These periods are real, but they do not always resolve on their own. Learn more about the 4-month sleep regression.
Nap transitions often trigger sudden night changes. When your baby is ready to drop a nap, the whole schedule shifts. Until the new rhythm settles, nights can become more unsettled. Read about how to manage nap transitions.
Teething and illness can temporarily disrupt even great sleepers. These usually resolve within a week or two once your baby recovers.
Separation anxiety typically peaks around 8 to 10 months and again around 18 months. Your baby becomes more aware of your absence and may protest more at bedtime or through the night.
A schedule that no longer fits is often overlooked. Babies grow quickly and their sleep needs change. What worked at 5 months may not work at 7 months. If wake windows, nap lengths, or bedtime have not been adjusted to match the current stage, nights can start to unravel.
What to Do
The first step is observing when the change happened and whether anything else changed at the same time. New skill? New environment? A nap dropped? Those clues usually point to the cause.
From there, resist the urge to make lots of simultaneous changes. Pick the most likely cause and adjust that first. Consistency over a week or two will tell you whether it helped. If you are unsure where to start, here is how I work with families to find and address the root cause.
Frequently Asked Questions
How long does a sudden sleep regression last?
Most developmental regressions last 2 to 6 weeks. If sleep has not improved after that, it usually means the schedule or settling approach needs attention rather than just waiting it out.
My baby slept through the night and now wakes twice — is that a regression?
It could be. But it is also worth checking whether the schedule has shifted. Increased waking after a period of good sleep is often a sign that a nap has dropped or wake windows need extending.
Should I change anything during a sleep regression?
It depends. If the regression is short and mild, staying consistent is usually enough. If it has lasted more than 3 weeks, a small schedule adjustment often helps significantly.
Can teething cause night waking for weeks?
Teething discomfort tends to be most acute when a tooth is actively cutting through — usually a few days at a time. Weeks of disrupted sleep are rarely caused by teething alone.