Macbook Pro Screen turns black and then Brings me to Login Page
A few times a month, my macbook screen randomly turns black and then a few seconds later, it brings me to the login page. After I log in, I find that everything has restarted like I have just restarted my macbook. However, it doesn't seem like my macbook restarted because every time this happens, Google Chrome tells me that it didn't shut down properly. Please help ASAP because it happens so unexpectedly and sometimes this happens while I'm working on a project which I haven't saved yet!
MacBook Pro 13", OS X 10.11