You are but assuming what I said is true you are not clicking here and there, meaning you are not refreshing the page. You are staying on the same page, even though you are typing, but the system thinks since the page has been the same for sometime, you are inactive.
Whenever you type a long post, it’s always advised to copy the post first. That way if you lose it whether due to system logging you out or internet crashes, you can always paste it.