Detective - Drunken PI hallucinates giant snake at high school. Read around late 1990s.

[Norman]

Circa late nineties, I read a detective novel about an alcoholic PI who was staking out a high school, one of those back east that have basements and second stories. He hallucinates a giant snake going into the school, and runs in after it with his pistol in his hand. He runs in, tumbles down the stairs into the basement level and knocks himself out. He wakes to find the principal standing over him with the pistol in his hand. Realizing what he did, he lies and says he saw the suspect enter the school and gave chase.