The Big Bang Theory Episode 1.04 The Luminous Fish Effect

Sheldon is fired from his job as a physicist at the university when he blows up at his boss who he thinks is not a smart as he is. His change of circumstance sends him into a downward spiral of depression which the boys try to cure by sending for Sheldon's mom. When his mom arrives for a visit, the boys realize his mom is completely the opposite of what they expected. They would never have guessed Sheldon was related to her as she is simple and sweet. But the visit works, and Mom is able to successfully get Sheldon back on track.