No. That feeling does not mean your body functions were about to stop.

It is usually a normal hypnic jerk (also called a sleep start): a brief involuntary muscle jolt as you transition from wakefulness into sleep. It can come with a vivid sensation of falling, then wake you abruptly. Sleep medicine texts describe it as a normal, non-pathological phenomenon that commonly occurs at sleep onset, experienced by roughly 60% to 70% of adults. Bradley and Daroff's Neurology in Clinical Practice describes sleep starts as physiological and without pathological significance.

One theory is that as muscles relax while falling asleep, the brain may misinterpret the change as falling and trigger a sudden muscle contraction. It is not a protective response to imminent heart, breathing, or other body-function failure.

They can be more likely with:

Consider medical advice if the jerks are frequent enough to disrupt sleep, happen repeatedly during full wakefulness, involve loss of consciousness, injury, unusual confusion, chest pain, fainting, or waking gasping/short of breath. Otherwise, an occasional episode is generally harmless. The Sleep Foundation overview describes the same falling sensation and common triggers.