I love that feeling when an inkling of a tune, a riff or chorus comes into my head 'just like that.' It may be a day, weeks or months before I put the words and tune and arrangement together. As a re-enactor, these days I play in a period band and have managed to include original songs with songs that were written in the 19th century. On CD's and in performance, they blend in well. Write what you feel in the genre you play and be thankful for the gift.