WordPress software has an autosave feature that saves every 2 minutes. Each time you click Save Draft or Update Post (or Page) a revision is saved.
<p style="padding-left: 30px;">In your Dashboard view, on the upper right corner, under the “[name]” is a tab labeled “Screen Options.” Click it. Here is a list o f the screens where the modules can be hidden:
Posts – Post Tags, Categories, Excerpt, Send Trackbacks, Discussion, Comments, Post Slug, Post Author, Post Revisions
Page – Page Attributes, Recommendations, Featured Image, Discussion, Comments, Slug, Author, Revisions
Select those and return to your Dashboard.</p>
<p style="padding-left: 30px;">Make sure you select Select Post Revisions and Page Revisions those and return to your Dashboard. Then close the tab.</p>
<p style="padding-left: 30px;">On the left toolbar, click on either "Pages" or "Posts" depending on what type of document are you are trying to restore.</p>
more here > Recovering a lost post or page