Don’t rule out attempted suicide. “Maybe”, he is enduring withdrawal from drug addiction.
Without knowing more than the powers that be let out, there's only speculation.
As far as it being an actual murder attempt, I'm skeptical. The guy that they showed as being in the jail cell with him could have killed him with an unsharpened pencil.
Warning? Possibly, but if it was done as a warning, it's only because too many people around the Clintons have already died in mysterious circumstances, and this one would be harder to cover up.
Self-inflicted? Possibly, as it could assist his lawyers, who are trying to get him bailed out, by claiming he's not safe in prison, and should be home with his own guards.
There's also the possibility his cell mate didn't like him and just beat his butt, cause he's a rich guy that got away with everything forever. Never underestimate how much the blue collar criminals hate the high dollar guys that get away with everything.
The premise of him going through drug withdrawal is an interesting take, but wouldn't explain the injuries. Just being locked can make a guy psycho, even if he doesn't have drug addictions.
Very unlikely: He was a devotee of healthful practices; immoral eroticism was his major vice. He reputedly was a teetotaler, or close to it.