I use the term "obsession" when describing my special interest, and for a reason - that's what they are, for me. When I'm really into a special interest, it usually consumes every thought I have throughout a day. There really isn't much of a choice but to engage in it in some way. This is really a problem when I occasionally become obsessed with something I don't actually like. I was obsessed with the band Slayer for a few weeks and felt compelled to listen to their music and learn all the lyrics even though I don't actually like it. Or more recently, I happened upon a movie called Thanatomorphose - basically watching a woman rot while she's still alive, plus bonus sex. I haven't seen the movie, and I don't ever want to see it, but I felt compelled to learn absolutely everything I could about it and if I had easy access to it, I probably would have watched it even though I didn't actually want to (I'm very glad I didn't).
When it's past that initial "complete obsession" stage, I continue to engage in my special interests because I enjoy them and since I have no job, no family of my own, not even a place of my own, I oftentimes don't have much better to do. I can easily have several hours go by in what feels like no more than half an hour while engaging in a special interest. I haven't been fortunate enough to get special interests that are actually useful for anything, but they make me happy (usually). There's a sensation I get from engaging in a special interest that I can't really explain, but it's definitely a positive feeling.
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Yet in my new wildness and freedom I almost welcome the bitterness of alienage. For although nepenthe has calmed me, I know always that I am an outsider; a stranger in this century and among those who are still men.
-H. P. Lovecraft, "The Outsider"
When you assume, it makes an a** out of u and me.