Why do i feel sad all of a sudden? could it be bipolarism?

Maybe: Sudden sadness by itself is not bipolarism, or even depression, just like a cough is not necessarily pneumonia. There are several reasons for sudden sadness. Depression, and bipolar depression, has sadness plus a group of associated symptoms occuring together over a defined period of time. If the sadness persists for no clear reason, if you have other symptoms or fears, consult our doctor soon.

Depression: Get an evaluation from a psychiatrist to help identify what depression/bipolar means to you and whatever else may be bothering you. Consider recommendations for medication if any are given. Get a referral for a reputable psychotherapist to speak with. Meds and therapy combined are most optimal; no just one or the other.