There's no nice way to say it — sleep regressions suck. It is incredibly frustrating for everyone involved when your baby suddenly stops napping or sleeping, but knowing why does sleep regression happen can make you feel a little more in tune with your child and their needs. (But you'll still be exhausted, sorry about that.)
First of all, you need to determine what a sleep regression actually is. Your kiddo fighting about a nap one day and then sleeping fine the rest of the week is not a regression. Your baby waking up, consistently, one time per night and going right back to sleep isn't a regression. According to The Sleep Lady, a sleep regression is a period of time when your baby starts waking frequently throughout the night and even skipping their normal nap routine, when they were once sleeping just fine. These regressions can last anywhere from two to six weeks before your baby finally gets back into a sleeping pattern. They can also happen more than once and many parents can attest to regressions happening at 4 months old and 8 months old according to the Baby Sleep Site.
Super frustrating, right? But your baby's not just trying to ruin a good thing — they are just growing. Pinky McKay, an International Board Certified Lactation Consultant, noted on her website that sleep regressions should actually be called sleep progressions. Your baby's sleep is disturbed for a couple of weeks at a time, before going back to a normal schedule, because of their development. She noted that these developments can be physical, like crawling, emotional, like having separation anxiety, and neurological.
The Baby Sleep Site agrees, suggesting that every sleep regression from the 4 month old sleep regression to the 18 month old sleep regression are connected to your child's development. Whether their lack of sleep is from cutting teeth, being too stimulated and busy during the day, or because they're outgrowing a nap, their sleep is changing because they are simply growing.
I know. It doesn't make it much better. But when you remember that there is an end in sight and you know why a sleep regression happens, it can make you a little more prepared (and patient) for those 3 a.m. wake-up calls again. The Sleep Lady suggested not only staying flexible, but be sure to not introduce any new sleep associations as a way to catch some extra Zs. That's just asking for more sleep trouble down the road and, trust me, once all of the regressions are done, you won't be prepared to wean your child off the rocking chair and into bed.