The Situation Enters Rehab -- Hit Rock Bottom While Taping 'Jersey Shore'

Multiple sources close to The Situation tell TMZ ... the MTV star's hard-partying ways were worse than ever during the taping of the most recent season of "Jersey Shore" ... and the signs were obvious during the episode when the gang went camping.

TMZ broke the story ... Sitch recently checked into rehab for substance abuse after realizing his recreational habits had spun out of control.

Now, sources close to Sitch tell us ... the reality star had been showing signs of substance abuse for a while ... but "he was getting worse" as the season went on.

We're told ... several people noticed he was "acting paranoid" on the set ... and the unusual behavior was evident in certain Season 5 episodes that recently aired on MTV. During the ep when the gang goes camping, Sitch can be seen acting jittery, sweating profusely and just plain acting bizarre.