Sid like his friend, and Mork's pen pal, Peter Panofski, is a resident of Happy Valley Sanitorium, who Mork encounters when he goes to visit Peter in Season 3's Mork in Never Never Land.
About Sid[]
Grumpy Sid is a resident of Happy Valley Sanitorium, whose closest thing to a friend is his fellow inmate, Peter. His friendship with the perky Peter is such that the grumpy Sid is actively disappointed when Mork arrives for him, as Peter's upbeat optimism irritates him and it means Peter has another friend.
He is doubly irked when Mork enthuses wildly about the Sanitorium, not understanding in the slightest the purpose of the rubber rooms and wire grates over the windows. Mork & Peter try to get Sid to play games with them, but he resentfully blows them off. When Mork immediately believes that Peter is, as he claims, Peter Pan, and tries to get him to come home with him to cheer up a depressed Mindy, Sid almost cheerfully reminds him that he can't leave the Sanitorium.
And it is Sid again, who stands in the way when Mork tries to break Peter out of the Sanitorium later that night, Telling Peter that Mindy needs him. When Mork tells him that Mindy believes he's from Ork, Peter resolves to go with Mork, even when Sid discovers them. He threatens to blow the whistle on them, but in the end lets them go, and pretends not to be impressed or even surprised when Mork uses his finger to cut through the wire mesh over the windows.
When Peter is tracked down to Mindy's Apartment, it is the news that Sid misses him that actually stops Peter from trying to run. Peter hearing his friend needs him, the reason he returns back to the hospital.