Just know that, per age stages and developmental stages.... "sleep patterns" in EVERYONE, changes. It is not set in stone.
No adult person sleeps the same way now, that they did when they were a baby.
And no baby, toddler, child, Pre-Teen, Teen, College kid, Adult, or elderly person... has slept the same way with the same patterns, since they were a baby.
It changes.
And sure, the natural stages of development, such as separation anxiety... just is. We cannot turn it off or on at-will. It is a developmental stage. Just like night-terrors or dreams, or nightmares or teething.
I always just went according to my kids' cues for sleep, or comforting needs, when they were a baby and even now. And they sleep well, they were regular nappers, and there was hardly any sleep battles. And each of my kids, were different per sleep/naps.
Also, being over-tired or over-stimulated, can really abrupt or disrupt a baby's sleep. Babies or kids do not instinctively know how to keel down or wind themselves down.