Are there facts or clues that you are still entrusting to your memory? Never assume that something is "impossible" to forget. This temptation is greatest when researching a distance away from home. Don't wait to "write it down later to save time." It may take a little time during your research trip to write down "why" you copied something or "how" you reached a conclusion, but that time is well spent.
Waiting until you get home is only asking to forget.