Story highlights A former bath salts user says his overdose was the worst experience of his life

"You feel like you're 10 feet tall and bulletproof," Freddy Sharp says

"Bath salts" are in the spotlight after a grisly recent crime in Miami

The man is strapped onto a gurney and restrained, yet he is singing, making faces and twitching.

"You know where you're at?" a paramedic asks him, but Freddy Sharp can't answer. He was, he explained later, off in his own world after overdosing on synthetic drugs known as "bath salts."

"I'd never experienced anything like that," Sharp told CNN's Don Lemon. "It really actually scared me pretty bad."

He said he was hallucinating about being in a mental hospital and being possessed by Jason Voorhees, the character from the "Friday the 13th" movies.

"I just felt all kinds of crazy," said Sharp, now 27, of Tennessee, who says he hasn't used bath salts in months.

"It felt so evil. It felt like the darkest, evilest thing imaginable."

The drug made national headlines recently after a horrific crime in Miami , where a naked man chewed the face off a homeless man in what has been called a zombie-like attack.

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Video footage captured by surveillance cameras on the nearby Miami Herald building shows the 18-minute attack , which ended when police shot and killed a man identified as Rudy Eugene, 31.

The footage shows a man walking along a sidewalk and stopping in a shaded area created by the tramway bridge. He apparently attacks the victim, dragging him out from the shade, stripping the victim's clothes off and beating him as the victim kicks his legs in an apparent attempt to fight back. He then spends several minutes crouched over the victim.

"The guy just kept eating the other guy, like ripping his skin," witness Larry Vega told CNN affiliate WSVN.

Police told CNN affiliate WPLG that when officers arrived and told him to stop, the man growled like an animal and continued eating the victim's face.

Authorities said they suspected the attacker was under the influence of bath salts. The victim is in critical condition at a Miami hospital.

Not the same substance used to scent your bathwater, bath salts contain amphetamine-like chemicals such as methylenedioxypyrovalerone (MDPV) and are sold as "cocaine substitutes" or "synthetic LSD." Its effects include paranoia, hallucinations, convulsions and psychotic episodes.

"This is a terrible drug because it takes a combination of methamphetamine, and the paranoia and the aggressiveness, and LSD, the hallucinations, and PCP, the extreme paranoia that you get, combines it into one, and has unpredictable effects on human behavior," Paul Adams, an emergency room doctor in Miami, told CNN.

The drug remains legal in some states, although many others have taken steps to ban the substances.

But sometimes, when one chemical used in bath salts is banned, another chemical is substituted to skirt the law, said attorney Alex Manning.

"People are making this stuff out of household products, stuff that's in their kitchens," she said.

It can take "five or six grown men" to restrain a bath salts user, she said. "It's PCP on crack."

And cases are on the rise, Adams said.

Police in Panama City, Florida, said last year they had seen two violent incidents linked to use of bath salts. In one, a woman allegedly tried to behead her 71-year-old mother; in the second, a man on bath salts used his teeth to tear up the back seat of a patrol car.

Sharp said he never felt the urge to "eat anybody's flesh" while under the influence of bath salts, but noted, "You feel like you're 10 feet tall and bulletproof, and you actually do not feel any pain."

He said he himself "just got paranoid."

But he said his overdose -- was a turning point, describing it as "Fear. Darkness. It felt like impending doom was coming down on me ... I felt like I was about to bust loose and actually hurt somebody."

He recalled trying to calm himself unsuccessfully. "I felt like if I lost that control, anything could happen," he said.

The experience, he said, was the worst of his life. And coming off the drug was also difficult, he said. Besides the withdrawal, "whenever it comes out of you, you can smell it in your hair. It's so nasty." He described the smell as a "unclean, nasty, unkempt, chemically-type smell."

Asked what he would say to other users, Sharp said, "The only thing I can say to them is that if you value your life, you'll stop it and you won't do it anymore, because it will destroy your life. It will destroy your family. It will destroy everything."