To become really chill or relaxed due to a satisfying or overwelming meal, but not so much that you want to pass out, but rather chill out. The following activities that can occur from the following chill session can vary from; watching TV for hours, to playing video games for hours, to smoking weed and eating snacks (resulting in longer lasting effects of the chillitis, yet still no sleeping).
This word is a combination of chill and itis.
Itis, for the most part, results in sleep. While Chillitis results in lazyness and minimal activities.
Nigga A: Yo B, that meal got me still, I think I got the itis...
Nigga B: You feelin' you gonna pass out? There's a bed upstairs.
Nigga A: Naw man, just, you know... chillin', not really tired...
Nigga B: That ain't no ordinary itis, that's what we call "Chillitis".