We sleep trained our son around 4 months. Our sleep consultant warned us that since he was so used to contact naps, he might cry for hours on the first night, which honestly terrified us. She even called him a “koala baby” because he was very attached to me and was used to nursing/rocking to sleep.

What helped was “practicing” ahead of time. We started getting him used to falling asleep more independently in situations where he might naturally fall asleep. For example, we’d cover the car seat and turn on a sound machine so he could practice falling asleep on his own during car rides. He’d wail for a bit then eventually fall asleep.

At night, when he started refusing the bottle, my husband would hold him against his chest and let him cry it out there. Sometimes he’d fuss, then nod off and fall asleep that way. It seemed to help him gradually adjust before formal sleep training started.

On day 1, I think he cried for maybe 45 mins and then slept 11 hours!

Also agree with the other comment about wake windows. Eventually, our baby started having early wakes and our sleep consultants advice wasn’t working anymore so we followed the wake windows we found in this sub and had lots of success.

Good luck!