There's nothing very firm to be said on the subject one way or the other.

On the one hand, some geological evidence has been found that's consistent with an ancient report of fumes that came from a crevice over which, or next to which, the priestess sat -- though that report specifies that the fumes were sweet-smelling. So there's that.

On the other hand, the Oracle did not have a vivid imagination. Are you thinking of oracles of the kind reported in Herodotos? They are virtually all fictional, invented after the event, and not even a tiny bit representative of what actual oracles looked like. The fictional reputation is that oracles were poetic, metaphorical/obscure, and ambiguous. Actual oracles -- about which about half of our reliable evidence comes from inscriptions, not from literary sources -- were none of these things: reports consistently make them straightforward yes-or-no answers to yes-or-no questions, usually asking the god's advice on an important choice or asking for the god's go-ahead on some religious matter. There is exactly one plausible report of a poetic oracle prior to the 2nd century CE; after that point we get another half-dozen reports, which together indicate that at that time the Oracle's reputation for ambiguity and impenetrability had begun to affect the actual practice of the Oracle.

More details in this older post. It seems likely (though the evidence is not clear) that the fictional oracles we see in authors like Herodotos are either borrowed from, or imitations of, a group of poetic collections that were circulating at the time under the authorship of "oracle collectors" who probably had little if any link to Delphi: people like Bakis, Epimenides, Onomakritos, and others. These poets had a very mixed reputation in fifth-century-BCE sources: Aristophanes satirises them mercilessly, Thucydides mostly adopts a tone of slightly scornful scepticism (and reports on fury at the oracle collectors after the failure of the Sicilian expedition in 413), and even Herodotos is scathing about some oracle collectors, while wholeheartedly approving of others.

Maybe.

"Whenever, then, the imaginative and prophetic faculty is in a state of proper adjustment for attempering itself to the spirit as to a drug, inspiration in those who foretell the future is bound to come; and whenever the conditions are not thus, it is bound not to come, or when it does come to be misleading, abnormal, and confusing, as we know in the case of the priestess who died not so long ago... She was like a labouring ship and was filled with a mighty and baleful spirit. Finally she became hysterical and with a frightful shriek rushed towards the exit and threw herself down". (Plutarch, Moralia 438.51)

Plutarch himself compares this rapture to the effects of a drug. However, this sort of behavior was not considered to be normal for the Pythia.

"It is a fact that the room in which they seat those who would consult the god is filled, not frequently or with any regularity, but as it may chance from time to time, with a delightful fragrance coming on a current of air which bears it towards the worshippers, as if its source were in the holy of holies; and it is like the odour which the most exquisite and costly perfumes send forth." (437.50)

Plutarch mentions the fragrance filling the room which some modern scholars believe to be a ethylene gas leaking from below. There are a number of studies that have confirmed some amount of the gas present at Delphi.

Luiz Caldas posited that the laurel leaf crown could cause a form of intoxcation: Caldas, Luiz. “The Laurel Leaves Toxicity May Also Be Responsible for the Trance of the Delphic Pythia.” Toxicology Letters 180S (2008): S231-232.

Chong has posited that the Pythia's erratic behavior is because she was selected for the role because of some sort of mental illness: Chong, M.S. “Possession by Malign Spirits? An Organic Explanation for Bizarre Behaviour in 2 Young Women.” Journal of the Neurological Sciences 285 S1 (2009): S155-S339. P. S242

Ultimately the answer is pretty unclear if the Pythia was drugged or not. There is healthy debate over whether the Pythia herself even gave the Oracles or if the male priests (prophetai) who surrounded her actually created and or delivered the messages. Personally I think it varied over the years. There might have been an occasion when the air currents let ethylene gas build up near the Pythia's seat and she got high as a kite that day. One or more of the Oracles might have been mentally ill. Everyone has a bad day at work... and you've got a whole line of Oracles throughout the ages with their own personalities. Not to mention that Greek attitudes toward women evolved a bit over time... it's possible the Pythia had greater or lesser autonomy depending on the era and her own capabilities.