Learn Spanish (Latin America): No deberías obsesionarte tanto; te dio por ayunar todo el día. - You shouldn't obsess so much; you've taken to fasting all day.

The structure darle (a uno) por followed by an infinitive is used to describe a sudden, often unexplained or capricious whim to start doing something. Literally, it translates to something like "it gave you to fast." The verb dar is always conjugated in the third-person singular (here, the preterite dio), and the person having the whim is the indirect object (te).

Why is dio in the preterite tense if the English translation uses the present perfect ("you've taken to")?

Spanish uses the preterite dio here because the phrase focuses on the exact past moment when that sudden, capricious urge struck you. English often prefers the present perfect to emphasize that the new habit is still ongoing, but the Spanish expression emphasizes the sudden onset of the whim in the past.

Why do we need the -te at the end of obsesionarte?

The base verb obsesionar means to cause an obsession in someone else (e.g., a movie obsessing a fan). Because you are talking about the person becoming obsessed themselves, you must use the pronominal form obsesionarse. Since the subject is "you," we attach the matching pronoun -te directly to the infinitive.

Why isn't there a que after deberías, like there is with tienes que?