We do not even have control of our own thoughts and emotions so how do we expect to control another human being? The more we try to control and it does not work, the more stress we have. When we let go of the idea that we can control our children, and their sleep, the stress starts to disappear.
A baby has six arousal states - being asleep, drowsy, hypo-aroused, calmly focused and alert, hyperaroused, then flooded. When a baby gets to the point of being hyperaroused or flooded, they are burning a lot of energy. The only way to help them out of this state is to help them down-regulate and this involves PARENTAL CONTACT/SUPPORT. It is not something that can be done by leaving a baby/child alone. They cannot up-regulate themselves or down-regulate themselves. If a parent does not help them down-regulate in their hyperaroused state, they will go up the arousal scale, become flooded, and at this point, the baby burns so much energy that they may fall asleep - NOT BECAUSE THEY SOOTHED THEMSELVES, but because they are passing out from sheer exhaustion. "It is the brain's last mechanism for protecting itself from severe energy depletion." Dr. Stuart Shanker, 2016