The 25-year-old man was crushed under the weight of a Remondis truck on Beveridge Street about 10.30am Monday.

He suffered a suspected fractured pelvis and a fractured right leg with a horrifying degloving injury - where a significant amount of skin and tissue are ripped away from the underlying muscle.

The man remained conscious and became loud and hostile as paramedics came to his aid.

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NSW Ambulance duty operations manager Norm Rees said extra paramedics were brought in to tend to distressed onlookers.

"As a result of misadventure, and believed to be under the influence of some recreational drugs, [the man] has gone under the garbage truck," said Insp Rees.

"It was quite chaotic when we got there, a number of bystanders required our assessment.

"They were quite distraught. I guess for the people that don't see it all the time, it is quite distressing.

"[The patient] was very distraught with the pain. He was obviously hallucinating and a little bit combative."

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The man was taken under police guard to Shellharbour Airport, then flown to St George Hospital.

Inps Rees said the man needed to be sedated before take-off.

"If the patient becomes aggressive during flight it can cost a lot of lives, so we have a procedure we follow to make the patient stable during flight," he said, adding the man's leg could likely be salvaged with lengthy rehabilitation.

Meantime, the truck driver walked away physically uninjured but visibly distressed.

He was embraced by a Remondis representative as he emerged from an ambulance later Monday morning.

"[He was] just doing his job and this happens; it's a bigger picture there's more people to treat than just the one patient and we're always aware of that," Insp Rees said.

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A resident who witnessed the aftermath told the Mercury she remained too distressed to discuss what she had seen.

"Every time I talk about it I see it again," she said.

"I'm trying to forget it."

The Mercury understands the man was a visitor to the neighbourhood and was not a resident.

Dr David Caldicot, an emergency consultant based in Canberra and a senior lecturer at ANU Medical School, said psilocybin mushrooms, commonly known as magic mushrooms, could affect different people in radically different ways.

"There's a lot of people who use magic mushroooms around Australia who don't suffer bad effects, but they're generally consuming them in an environment that they find safe or pleasurable or with people that they love," he said.

"The mindset you're in - how you feel about the world - and where you are when you're using these drugs has a huge impact on what your experience is going to be."

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"That's part of the problem - it's impossible to predict for any person. It's very hard with an unregulated product where you don't know how it's going to effect you - and the more potent the drug, the more potentially hazardous.

"These are very, very potent products, so they would not require you to sit down and graze in a field. Several mushrooms might be effective."

Dr Stephen Bright, a senior lecturer of addiction at Edith Cowan University's School of Medical & Health Sciences, said it was highly rare for someone to suffer serious injury after consuming psilocybin mushrooms.

"Of the rare cases where there has been serious injury due to misadventure, often there have been co-morbid mental health issues," he said.

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