Season 1

Thomas Sanders decides to take some time to figure himself out, and introduces three different parts of his personality: Logic, Morality and Creativity (also known as "Princey").

Thanksgiving is approaching and Thomas' dad, his real dad, has asked him to help cook the turkey. But Thomas still doesn't know how to cook, so Morality pops up and reminds him that he should improve on the process of becoming an adult, which he consistently calls "adultery", to Thomas' dismay.

Thomas is feeling quite relaxed, when suddenly Anxiety pops in and ruins his peace. He calls for help on Creativity, who suggests Thomas to retire to a corner of his mind for reinforcements. He does so, and Thomas and Anxiety pop up on Lilly Singh's apartment, where she gives Thomas a few tips to, if not destroying Anxiety completely, at least bring him down enough.

New year has arrived, and as suggested by Logic, Thomas starts thinking on New Year's resolutions. Creativity and Morality also pop up to give suggestions and in the turmoil of emotions, Anxiety pops up to remind him that it is pointless to waste time on New Year's resolutions because he's going to give up fulfilling them in a month or probably less.

Thomas has decided to talk about the messages given by Disney movies, so Princey, as a Disney fan, cannot help popping up. So does Anxiety as he too is a Disney fan, because he sees the sinister undertone messages that Disney movies also provide. So Princey and Anxiety start a debate about what positive or creepy messages can be inferred from each Disney movie.

Thomas has fulfilled one of the dreams of his life, appearing on a Disney show. So the Sanders Sides appear to ask him how the experience was.

Thomas decides to have a talk with Logic and Morality. They both collide so much that they make him feel confused in his daily life, and he gives them a few examples of situations when this has happened.

Valentine's Day is coming, and Thomas is single and without hope of getting a romantic date on time. His Sides give him advice about how to approach romantic relationships, using a projection of Thomas' friend Valerie as an example of romantic crush.

Thomas has nothing to talk about. He's been procrastinating so much he didn't get anything on time, so Logic decides to discover in a Sherlock outfit, who among the Sanders Sides is the culprit for Thomas' procrastination.

Thomas asks his followers on Twitter to send him questions that the Sanders Sides will answer as best as they can.

Thomas decides to show a series of drawings about his life, when Anxiety pops up and tells him that's boring because it is a "Draw My Life" and is something that lacks originality. So Creativity pops up and sets "Daydream Mode", where he'll be in full control to brainstorm and try to get to a really completely original idea. But all the ideas they get are versions of things that have already been done.

Thomas has just had an audition where he forgot the lyrics of the song he had to sing. Tortured by this blooper, and since Roman is too bruised for what happened and Dad is taking care of him, he calls on Logic for help while Anxiety keeps torturing him on the failure he has incurred into. Logan soon realizes that Anxiety is putting into Thomas' mind a number of cognitive distortions that are making Thomas see things worse than how they probably really are. So, Logan decides to set up a formal debate between him and Anxiety with Thomas as moderator to help Thomas identify these cognitive distortions and put them into perspective.

It's been Thomas' birthday and he is wondering if he's doing what people of his age are or should be doing. Logan and Roman point out that Dad is acting as a slowdown on Thomas' adulthood and he should change his habits, forget everything that Dad provides him and act as a real adult. But the full abandonment of the simple pleasures of life provided by Dad only make him feel unhappy and depressed, so they realize something's wrong with their suggestions.

Thomas has just started using a new Mind Palace to have his conversations with the Sanders Sides, but for some reason he feels distressed about all the changes that he's going through lately and quickly pops back to his previous location, his apartment. There, Anxiety points out that the reason he's feeling that way is because he's too much time away from his friends and that he needs them in order to be consistent. Roman suggests that they could shape shift into Thomas' friends forms so that he could have them with him all the time no matter where he went, and Thomas changes all of them into their friends forms. Anxiety is the only one that doesn't want to be changed, but yet he is constantly being changed by the other Sides into four of Thomas' friends, Valerie, Joan, Terrence and Talyn.

Thomas talks about how he loves cartoons, and how he would love to be a cartoon. So, he decides to fly to L.A., meet Butch Hartman and ask him to turn him into a cartoon. He reluctantly does and for a minute Thomas and the Sanders Sides become characters of a day in the life of cartoon Thomas.

Thomas is acting strangely, like an aloof moron without common sense at all. He doesn't take care of his hair or his clothes, he has no filter on what he's ready to say about his private stuff, he loses attention of what the others tell him, and even he has lost his fear of death and survival instinct and reflexes. Logan notices this and calls Roman and Patton for help. Soon they all realize that he has no anxiety at all, and when they call him, Anxiety doesn't show up. So they decide to sink down, all of them, Thomas included, into Anxiety's room, the corner of Thomas' mind where Anxiety resides, to find out what happened to him.

Thomas and the Sanders Sides appear on Anxiety's room, which looks just like Thomas' apartment decorated as in a Tim Burton movie, with a clock that moves quickly backwards, spider webs everywhere, posters of "A Nightmare before Christmas" and a curtain with drawn spiders, something that scares Patton to death. At first they don't see him, but soon Anxiety pops up startling them all, a moment when Thomas goes back to normal. Anxiety tells them he has decided to quit, as he didn't thought he was wanted, and even though he only intended to protect Thomas, he has understood that he overdoes it and thinks Thomas will be better without him. Thomas and the others try to convince him to come back, as anxiety, even if unpleasant, is necessary for Thomas' life. But soon something strange starts happening to the Sanders Sides, as they start developing the same eye-shadow and progressively become more and more anxious the more time they spend on Anxiety's room.