I hate it when this happens to me! It happens way too often. Although it's obviously not how all of our favorite composers did it, using technology to record your improvisations or using a midi hookup to a computer would probably be the best thing to do.

For me, my improvisations are sometimes better than my written down compositions. I feel like what comes naturally out of my head can be better than something I have to think about a lot. Anyone else feel like this?