He didn't. The turbulence was heavy, and in it he accidentally swallowed his heroin stash.
Or he tried to swallow it on purpose because he was afraid to be discovered carrying drugs on plane and get arrested. That is the reason he ran in the bathroom in the original Oceanic flight as well.
He remembers the island, and didn't want to continue a sad life of drug abuse and a failed career.
Or he remembers the island, and died to see if he could get anyone else to remember.
His life is just simply horrible in the alternate timeline (or he perceives it to be) and felt no urge to live anymore
He tried to kill himself because he wants to go out like a rock star. "Driveshaft bassist Charlie Pace dies smuggling heroin" is what he wanted but instead it'll read "Driveshaft bassist arrested smuggling heroin"
In the normal timeline he would have killed himself if it wasn't for the turbulence.
He was swallowing the drugs in the small bag. He was obviously attempting to hide the drugs.
no he was going to flush the drugs down the toilet in the original timeline
no way, he was going to stash them or hide them on/in his person, no self-respecting junky would just waste that much dope (the bag is very large)
He was killed on the island in one timeline. The other timeline is where he tried to kill himself but lives.
in LA X part 1, we see that Charlie wants to die. Maybe in this timeline Charlie wants to die the whole time, but he can't. At the island he didn't want to die, but he had to. It's like Hurley who's now lucky insteade of unlucky.
Charlie visits Hurley at Santa Rosa in The Beginning of the End. Hugo's friend Lewis can apparently see him and comments that someone is staring. Therefore this is flesh and blood FS Charlie that has crossed timelines.