if it is a long post copy it before submitting. Nothing worse that spending 10 minutes trying to sound intelligent to have it disappear.
Luckily you don't really need to do that due to the auto save feature. Anytime you write something in a topic the auto save will save it and to retrieve it all you need to do is refresh or go back to it whenever you get around to it and it will be there even if it's days later. Look for highlighted in yellow, Previously entered content was automatically saved.
Restore or
Discard, click on restore and no matter what happens to you during the post, the text will be there for you the next time.
Unfortunately there have been some "new" unusual problems showing up this week making things even more difficult to use the forum. The tech crew is aware and will be looking into it as soon as they can. I know you've heard it a million times already but please continue being patient with the forums, everyone you help will appreciate it at the end.