Adenosine is a waste product of neurons and it is a potent nervous system depressant which is why if we don’t sleep for a long time we hallucinate, start to feel cold, and feel tired. We feel like we’re drugged because we kind of are. It also increases sleep pressure. Unlike other areas of the body the brain has no way of flushing out the adenosine unless we sleep which activates the glymphatic system. if we don’t sleep the adenosine keeps accumulating and it can kill us in a similar way an od of sleeping pills can.
Caffeine does this, but the effect is temporary. There’s a rare condition called Morvan Syndrome, where there is a case of a person with it going without any sleep for 4 months, and had no cognitive impairment. Normally a person would die after 11 days. Seems like this condition messes with the inhibitory synapses so it might also mess with how adenosine affects the brain as well. 10% of cases lead to death though