There is psychological approach called internal family system, it explains personality as collection of entities that cooperate unaware of each other. Perhaps some drugs disturb this to such extend that it feels like there are multiple people in consciousness.
If those external entities were real, we wouldn't need to wait for science, some shaman would just go to the spirit realm and get told about bacteria.
If those external entities were real, we wouldn't need to wait for science, some shaman would just go to the spirit realm and get told about bacteria.