I've lost 2 well thought out replies because I timed out before hitting the reply button.
It's a good habit to compose lengthy messages in some external application and then paste it into the browser. I typically use Wordpad for this. For shorter messages, I at least select all the text and copy it to the clipboard before submitting it.
it times out in the first place, and
When at other times, you can go to another page, go back on the browser to the reply page, and any text you types is still there.