As someone with a high signal lesion in the genu of the corpus callosum caused by childhood head injuries I think the brain split in two halfs is simply an impact "kill switch" for severe adult head injuries.

Ergo extreme impact trauma to the head results in the brain breaking the connections between the two hemispheres at the corpus callusom, resulting in immobolisation. However this could also be a temporary kill switch which immobolises the body until such time as the brain's neuroplasticity has restored the corpus callosum.

In such a condition the individual would likely be left for dead, be going hungry and quite likely thirsty which creates an increase in phagocytosis which in turn causes an increase in h2o2 and then catalase the enzyme from the liver breaks this down to water and oxygen, ergo the conditions to help the body live, if not in a slimmed down form (pun intended) still exists and lends credence to fasting.