It's about the subject. Kinda.

DU fühlst DICH schlecht. - (ты) чувствуешь себя плохо
DU erzählst über DICH. - (ты) рассказываешь о себе

It's easier if you learn the concept of СВОЙ/МОЙ etc. first (as has been highlighted by iCake above)- СЕБЯ then becomes obvious. Right, it's about expressing possessions, but in some way, it's related to the concept of how to express things that are related to the main person/subject.