I may say that these three states are strongly connected one with each other. Fixation is a sort of obsession, obsession is a sort of passion, but the thing that makes a difference between them is the intensity or the level these are reaching. Fixation has a lot of meanings, but when it becomes implanted in our brains, it would transform itself into passion. The more it captures the more is directed towards obsession.

Regarding the writings, I can say that most of us are filled with passion, our words are passionately. We write from passion and this makes us more connected with each other, opens in front of our eyes new perspectives, releases the anger we may have during certain periods of time, blossoms a carpe diem state of mind in most of the cases and the most important ... draws human inter-relations. It could be easy metamorphosed in a spider's web ... keeps us linked.

Anyhow, making one step further we reach the fixation level. This is the moment when our passion is like a tattoo engraved in our blood cells. There are lots of artists (writers, painters and so on) worldwide that created fixations from their passions.
Fixation becomes part of us, but it's not so strong as the obsession is - it's like being part of the sub-consciousness and escapes into the consciousness. This can have two side effects: 1. Makes us to go further, to enjoy the perfectional path it draws in front of ourselves - can help our writings (one of the passions most of us has, especially here) if doesn't exceed the normal intensity. 2. If it becomes too obsessive, then we reach the third level: Obsession.

This third state is a pathological one, and may have some OCD aspects. Depends on each individual if they’re like in a “no way back” state, or can return to the normal one.

Digging through all of them, some may write some interesting masterpieces.