Sleep suddenly fell apart? Answer a few questions and find out whether this is a regression, something else, and what to do next.
What this looks like
This tool gives general guidance based on typical regression ages and patterns. It's not medical advice: for illness, fever, breathing concerns, or anything worrying you, see your doctor. Every child is different.
A regression is a temporary dip in sleep in a child who was sleeping reasonably well, driven by a burst of brain development. The name is misleading, since nothing is going backward: your child's brain is leaping forward (new motor skills, language, separation awareness), and sleep pays the bill for a few weeks. The pattern: sudden onset, tied to a developmental window, and it passes.
The well-known windows: around 4 months (sleep cycles mature), 8 to 10 months (crawling, standing, separation anxiety), around 12 months (walking and language), around 18 months (independence, molars, separation anxiety), and around 2 years (fears, stalling, big life changes). Not every child has every one, and a child can sail through one window and get hit hard by the next.
Typically 2 to 6 weeks when the underlying sleep foundation is decent and the response stays consistent. Trouble lasting well beyond 6 weeks usually means the regression has ended and something else is holding the wakings in place: most often a new habit built during the hard weeks, or a schedule needing to grow with the child.
The change behind it is permanent, and that's a good thing. Around 4 months, your baby's sleep reorganizes from newborn sleep into adult-style cycles, with light sleep phases every 45 to 60 minutes for the rest of their life. The rough patch passes, but sleep doesn't return to the newborn version. What matters from here is how your baby falls asleep at bedtime, because that's what they'll look for at every light-sleep phase overnight.
Offer more comfort, and keep the shape of sleep the same. Extra reassurance, an earlier bedtime, and patience all help. The one caution: habits built at 3 AM are the souvenirs of a regression. Introducing a brand new way of falling asleep (feeding to sleep where you didn't before, a new bed-sharing arrangement meant as temporary) often outlasts the regression by months. Comfort within your normal pattern is the sustainable middle.
Illness and teething come with daytime evidence: fever, a runny nose, ear pulling, visible gum swelling, drooling, changed appetite, discomfort during the day too. A regression shows a happy, thriving child by day (often one busy with a new skill) whose sleep alone has fallen apart. Sick children need comfort first and schedules second; the sleep piece sorts itself once they recover, usually with a few nights of gentle reset.
Regression, habit, schedule, or a mix: from inside a sleep-deprived household these genuinely look alike, and the right response differs for each. Figuring out which one a family is dealing with is the first thing I do with every client. Hit reply to the email where you received this link and tell me what your nights look like. Helping families sleep is what I do.