If you feel like you’re falling when you’re sleeping, here’s what it means – Page 2

One explanation suggests that when the body relaxes very quickly when falling asleep, the brain can “interpret” that sudden relaxation as a loss of control or body support. In response, it triggers a muscle contraction, which manifests as the sensation of falling.
Another hypothesis takes our ancestors as a reference: when they slept in unstable or vulnerable conditions (for example in trees or rocks), a reflex to protect themselves from a real fall could have remained in our nervous system as a vestige.
It is important to note that this phenomenon occurs mainly at the onset of sleep, not during the deepest phases. This strengthens the idea that it is linked to the transition between wakefulness and sleep.