"Demonization" (daemonizimai) is ABSOLUTELY possible, and Probably a good deal MORE Prevalent that we know, or are willing to admit.
"Hollywood demons", of course are INFINITLY more powerful than the Hollywood "God", so "media presentations" of Demonization are ALWAYS more utterly hopeless and horrendous than the reality of the situations - i.e. satan is a BEATEN ENEMY, and ANY Christian has authority over Him in Jesus' NAME.
The "Worldly answer" for demonization WILL ALWAYS BE "some form of insanity" (There are NO SUCH THINGS as supernatural Demons - or some such similar foolishness).
THE PROBLEM IS - that the "visible church" (Regardless of denomination) is morbidly AFRAID of the Demonic, and for the most part is completely unable to address it when they encounter it. The Catholic church WILL ADMIT it's existence, but treats it in a completely beaurocratic way which is all but WORTHLESS in terms of actually solving it.
However ANY BORN AGAIN CHRISTIAN moving in the power of the Holy Spirit is completely capable of DELIVERING, in the power of the Holy Spirit, one who has become demonized.
There are any number of "Gateways" to demonization - Ouija, coming into contact with a GENUINE Spiritist Medium, Playing with Wicca, Astrology, and simply saying "YES" to little stuff - which leads to saying "yes" to bigger stuff - etc.
Drugs, since they can lower one's defenses, and make them more susceptible to suggestion could be a contributing factor, but probably not the PRIMARY factor.
It sounds to ME as though you DID come into contact with one who was demonized, and may have had other factors (possibly chemical) aiding and abetting his behavior.
Back in the '70s, there was a woman in our church, whose sister was at the point of being institutionalized because of crippling FEAR that led the family to fear that she'd destroy herself to alleviate the pain. However the Pastor of our Assembly of God church (Claud Dewlan at Celina, Ohio), and the woman decided to give "Deliverance a try" as a "Last ditch effort" before the papers were signed, and she was gone.
Long story short, they went over to her house and confronted the demonic entity - the Pastor in English and the Woman (who had NO training, or previous exposure to the demonic) in her Tongue - she described the TERRIBLE ANGER against the filthy thing that was killing her sister and described "Pushing against it" in tongues - until it left. And her sister became completely "normal" instantly (in her right mind).
For several days afterwards, the sister's Piano would clank in the middle of the night, and there were footsteps heard, pounding on the walls, and Shadows with nobody there, which the sister knew (now) to "Rebuke in Jesus' name" which stopped them, and then all was at peace.
Last time I Saw the woman I asked how her sister was 30 years later, and she said everything was fine, and the Sister was serving the Lord in a Church, and no further "Fear Issues".
SO THIS WAS a case of a person bound to the point of Commitment into an asylum, but after having Deliverance from Demonization Ministered to her, instantly becomes completely O.K. and remains that way - long term.
The "World" says that: "There are NO SUCH THINGS as supernatural Demons" (or heaven or hell, or Judgement, or a Messiah that shed HIS BLOOD so that we could be saved from our sin).
The "World" doesn't know what it's talking about.