The Cambridge dictionary defines the two words as follow:
1. A Passion for something: an extreme interest in or wish for doing something
2. An Obsession: something or someone that you think about all the time.
While a passion is “extreme behavior” it lacks the indefinite time connotation. We all have passions but how many times have we given up on a passion after a while?
Obsessions stay “all the time” and are very often linked to psychologically unhealthy attitudes such as, fanaticism, father complex, idée fixe (psychology), psychical inertia, regression (psychology) or substance dependence.
In such a context, people may be reluctant to describe themselves as an obsessive. Nevertheless, when you’re having an idea that sticks to you wherever you go, whatever happens to you and can’t refrain yourself from thinking and acting on it, you’re obsessed.
My partner calls me a self- proclaimed artist. Are there any other? She refuses to decorate our main living spaces with my artistic productions (they’re banned to a barely used sleeping room), finds in general my art “difficult to access” and that I’m having delusional thoughts about my own geniality.
I also suffer from insomnia: very often I wake up in the middle of the night to work. I need extensive prodding to be lured out of my studio to attend some social (mostly artistic) event. Lately I’m also getting exasperated about the amount of time a “successful” artist has to spend on self-promotion, so I gave it up. Away with the marketing gurus who talk about finding my “niche”. If there exists a “niche” for my projects, it will have to find me. And as far I’m concerned: the world is my oyster (the marketeers probably hate that phrase).

People call me also crazy but it’s also extremely easy to understand why and ignore it. I can turn into a real insufferable prick when circumstances prohibit me for some extended period from working on my own projects. How long it may take, how difficult it may be, how high the probability of failure is; it all doesn’t matter to me when it’s about my artistic projects.
Passion made me start, obsession keeps me continuing. Even when the world doesn’t seem to bother too much about my creations, they bother to me. They give shape to my reality. To be or not to be.