I had that happen earlier today. A story idea strong enough to keep my attention for several hours. Good thing the rig was making a trip and I could relax. Well, relax except for the interruptions with stupid questions.
That's not all it's cracked up to be. My first book came out in February. The second is due out in November. At least all the editing and legal garbage are behind me on that one. I'm three quarters through with the third and half of that is at the editors. She and I now have a system that works for both of us until legal gets into it. This one is supposed to be ready by the second quarter of next year.
Writing smut is a piece of cake and a lot of fun compared to the real stuff. Why did I ever let people talk me into doing this? Oh yeah, those advance checks. Those things are evil I tell you, pure evil.
I did read somewhere that one should write because the love to write because even if one is published in hardback it may not pay the light bill for long.
When I get hooked by a story idea it practically consumes me. I can't sleep and little else runs through my mind until I get it completely writen. I enjoy it, but it is like a very intense drug that comes with a horrible crash when the lack of sleep and mental exhaustion finally catches up with me.
But other than that, yeah. It's great to write for the fun of writing.