At some point in time all knockouts end up becoming neurological. However below is a detailed explaination.
Caused by blunt trauma to the head resulting in bruising or damage to one or more areas of the brain as it collides with the inside of the skull. This can be caused by heavy impact to the skull such as a martial arts strike, a fall, car accident, etc...
Caused by a short circuit, overload, or imbalance in the central nervous system (involving both the parasympathetic and sympathetic nervous systems). This can be using Kyusho Jitsu techniques. It may also be caused by extreme stress, emotions, shock, or extreme trauma to any area of the body (a broken or crushed limb for example). This kind of knockout can also be chemically induced (alcohol, toxins, allergies).
Caused by limiting the oxygen supply to the brain. This can be caused by choking or strangulation involving the air supply, the flow of blood or both. It can also be caused by impact to veins or arteries causing a disruption in the flow of blood, or by dislodging plaque from the arterial walls causing clots. This is one of the reasons why we tend not to do KO's on persons over the age of 40. Other causes such as stroke, cardio vascular disease and respiratory ailments such as asthma are considered Cardio/Respiratory issues but may also be triggered Neurologically.
Below is a video example of a Neurological Knockout at Stomach 5