The human brain is extremely complicated and over time it has gained many genetic mutations, some which affect metabolism. Even a small change in DNA can cause a defect in the production of proteins, neurotransmitters and neurohormones. These changes in brain chemistry affect the way people perceive reality.
This can lead to people experiencing the surrounding world in a special way, they may feel derealization and depersonalization. These people doubt the world or even they themselves exist. Most of them find it unbearable to live in such a subjective reality which leads to constant uncertainty, anxiety, and fear.
Many of those who were not diagnosed in time and did not receive help they need, find a solution in illegal psychotropic and psychoactive substances that help them to feel fine for a short period of time.