I have just recently started writing on a regular basis but I am guessing that if I had lost my desire to write and then it suddenly returned, it would be great! I used to love to read books but recently I have not been finding the time to do so. If all of a sudden the desire to read returned, it would be wonderful because I have memories of enjoying my reading time. People change, technology offers so much more nowadays, and moods always shift from time-to-time. I've learned not to fight or resist or force a certain outcome. All is well, all the time. If your writing mood wasn't happy but you felt the urge to get your message out in some way, then it may be important to do so.
Good question. Thanks for posting it.