While Rue constantly yawning throughout the episode seems to be her most prominent sign of withdrawal, she also endures more intense symptoms such as extreme sweating, abdominal cramping, and vomiting.
Rue runs all over town in hopes of finding drugs, eventually ending up on Fez’s (Angus Cloud) doorstep. He immediately flags the problem and kicks her out; this leads to Rue robbing another house, escaping a police chase, and reaching Laurie’s (Martha Kelly) apartment.
Source: https://www.distractify.com/p/why-does-rue-keep-yawning