Zoned Out

For a short time, Mark's parents wondered if he was taking drugs, since he'd started to zone out a lot. They dismissed it, mainly since he spent most of his time at home, and concluded that he was just lazy. "You're grounded!" had lost its power, but they gave him frequent lectures based on, "All you do is eat and sleep".

They died in the night, once the alien parasite finished eating Mark up from the inside.