When the chemicals that were inhaled through one nostril, out-weigh the other nostril. This causes a chemical imbalance in the head.
He only railed one line but decided to do a second one on the other side because he felt a chemical imbalance.
A largely unfounded hypothesis used to push drugs as a 'cure' to mental illness. People are fooled into accepting what is essentially marketing as 'science' by smarmy ads, vague language, and constant rehashing of the idea that emotions are medical problems.
There is no evidence for any kind of 'chemical imbalance' from birth causing any kind of mental disorder, but the pharmaceutical companies would like you to think so.