4 month regression?

Just went through this! Honestly not sure if we’re totally even in the clear yet. It was exhausting and I struggled for sure! Ours was also paired with bedtime scaries where she would scream the second we went to her room. It lasted almost two weeks. Then the other night she went down all on her own. No tears and is now doing 5-6 hour stretches, eating then going back down. I’m sure we’re not out of the regression yet as she is trying to roll, but just remind yourself that it’s just temporary. Nap if you can. Ask for help from parents during the day to nap. I had a few nights where I ended up co sleeping with her in the spare room just to get through the night. We didn’t build a bad habit. They’re just babies who need our support and comfort as the world is scary.

We are going through this right now too. She always only contact napped and was unable to be put down since she’s a newborn. With the 4 month sleep regression we started training her gentle to fall asleep in the crib. It’s been a lot of comforting and exhausting for us but I think it helped that the schedule didn’t fell apart completely. We could also tell she was ready to get sleep in her crib independently. She started preferring going down in the crib instead of getting sleepy in our arms

I just learned that babies are just now going through actual sleep cycles (light sleep, deep sleep, rem sleep) and when they transition into a new sleep cycle they need what they fell asleep with to stay asleep during the transition.
Example: baby fell asleep into light sleep cycle with pacifier, but it fell out shortly after falling asleep, when they move into deep sleep without the pacifier they will wake up.
Same goes for falling asleep while eating or being rocked and held.